For an ancient place of worship whose worldwide renown is surely the envy of giant cathedrals in faraway lands, Rosslyn Chapel is of surprisingly modest dimensions.

Initiated in 1446 by the Third Prince of Orkney, William St. Clair, its construction proved a mammoth task, spread over decades and beyond the Earl's own considerable life span.

The chapel has been owned by the St. Clair family for almost 600 years.

Art historian, Lady Helen Rosslyn, is the wife of the present Earl, Peter St.

Clair-Erskine.'

Well, it's rather lovely to think it was my husband's family who actually built this chapel in the 15th century, which is extraordinary, and it's been in the family ever since, which is rather nice.

So, it was built by this man over here, Sir William St. Clair in 1446.

And I think really the inspiration must have been that he'd been traveling in France where there are a lot of cathedrals in this very ornate gothic style.

So he must have come back really inspired to build his own chapel.

But I think, for me being an art historian, you're always interested in the story behind places and what it tells you about the history.

And I think that's what's so wonderful about this building.

It's got a story all of its own.

A narrative.

When you step inside it, you really feel as if you're stepping into the Middle Ages.

It's like stepping into a medieval carving really.

'During an age when life expectancy was just 35 years, William died in 1484 at the ripe old age of 74, leaving unfinished his beloved chapel.

It's thought that its original design was for a larger cruciform-shaped building.'

This is just the end of what was going to be a bigger cruciform building.

During the conservation, our architect took me over to Glasgow Cathedral to have a look at it because he said "you will be amazed," and he was right.

Because the choir at Glasgow Cathedral is exactly the same layout as here.

Obviously, at Glasgow Cathedral it's much larger, because the whole building was built as planned and here we've just got a little choir.

But it does suggest that this was very much a format, a layout, for this kind of building.

'Symbologist and author of The Rosslyn Matrix and The Rosslyn Templar, Ashley Cowie, has spent years researching Rosslyn Chapel.'

(COWIE) Yeah, indeed it was meant to extend about another 90 meters to the west, and the largest part of the church was never built.

If you can imagine, it was a cruciform church so it was built like a cross.

What exists today is the head of the cross.

So what I always say is, you know, this is meant to represent man on earth, the cross, or Christ on the cross.

All that's been built is Jesus's head.

His body and arms were never completed.

And I think it's just as well he didn't finish it, to be honest.

This actually is a perfect size for a family chapel, after all.

'Despite its humble size, the chapel was a remarkable accomplishment and one that drew craftsmen from across the land to accommodation purposely built for them by the Earl in the tiny village of Rosslyn, which is situated less than a quarter of a mile from the chapel and just a few short miles from Scotland's capital, Edinburgh.

The result is an architectural triumph whose survival, despite centuries of disuse, is a testament to the quality of its construction.

Before Lady Helen became part of the Rosslyn dynasty, she studied art history at Oxford University before securing a job with international auction house Christie's.

And it was there that she first came across Rosslyn Chapel.'

What was really interesting to me, when I was working at Christie's, I kept coming across paintings and drawings of this tiny place, and it was Rosslyn.

Considering how small it is, it was extraordinary how many people had painted it.

And I think what had happened is that, because quite a long time, it was lying abandoned, so, of course, it's so beautiful and so picturesque, and it was overtaken by ferns and there were plants growing up everywhere.

So I think it really appealed to the romantic sensibilities.

'Although intricate carvings abound throughout the chapel, it exhibits a remarkable absence of design planning.

This gives it a sense of complex spontaneity that draws visitors back time and again to make their own new discoveries among literally thousands of figures and scenes cut in stone.

Pillars, beams, walls, floors, vaulted arches, roof lintels and everything else involved in holding up a 15th-century house of worship, 68 feet, nine inches long and 42 foot, seven inches high are literally covered in carvings, big and small.'

What's extraordinary is the places sometimes you find the most delicate, intricate carvings.

There's a keystone right up there in the roof that is so beautifully carved and, of course, we can't even see it from down here with a naked eye.

I saw it during the conservation when I was up on the scaffolding and they've even engraved the fingernails.

It's so delicate.

So, some of the rougher carving is down on this level.

And I think there was a sense in the 15th century that the nearer you got to God, the harder you needed to work to make your carving special.

'If there is a common thread running through the carvings, it's one of enigma.

Freemason symbols in a Catholic chapel, a Catholic chapel that survived the destructive Reformation.

There's an angel playing bagpipes.

There's what appears to be an elephant.

How many people in Scotland in the 1400s would have even heard of, let alone seen an elephant?

There's a farmer's wife rescuing a goose from the jaws of a fox.

A knight on horseback and a rope-bound Lucifer hanging upside down.

There's a star-of-Bethlehem shining over Christ's Nativity scene and at least 100 Green Man pagan faces pulling the oddest of expressions.

There's also maize and corn, carved a century before Columbus discovered America, the only land where maize and corn existed at the time.

Perhaps the most striking carving and certainly the most discussed, is the Apprentice Pillar.

A stunning example of creative stonemasonry, encircling one of the chapel's 16 pillars.'

The master mason, apparently, when he came to the last pillar in the chapel, wanted to make it really special.

So he decided to go off to Rome, to do a bit of fieldwork and to get some inspiration.

And while he was away, his apprentice had a dream and he saw this wonderful pillar with a wreath of foliage wrapped around it, and he created it.

And when his master came back, rather than being pleased with his apprentice's work, he was so angry and so jealous that he killed him on the spot.

And what's rather lovely is, that the heads of the apprentice and the master mason, and the grieving mother of the apprentice are all carved in the chapel.

So the masons wanted to record this story in stone.

(COWIE) I've seen many, many pillars, many cathedrals around the world and I've never seen anything so ornate as that.

What's the most beautiful thing about it is, it's not been done with modern tools.

It's done with the eye.

The perspective, the ratio, the design, the proportion is all by how it looks.

If you look at that pillar, it's almost like it's been computer-crafted.

It is craft skills beyond anything else that exists in Scotland, that's for sure.

'As author of Rosslyn Chapel Decoded, John Ritchie explains that Scotland's greatest poet may have had something to do with the apprentice tale.'

It was never called the Apprentice Pillar until Robert Burns visited Rosslyn and gave Meg Wilson who was the landlady there, a story.

So it was really one of the first sort of tourist spins ever.

Let me tell you about the pillar itself.

A lot of people reckon the Holy Grail is under there.

A lot of people say the head of John the Baptist is under there.

I've been involved in scans of that pillar - there is nothing inside that pillar.

The beauty in the mystery and the secret, and the true knowledge of the ancients is on the outside in plain sight.

'Facts being manipulated to shore up a questionable story that is impossible to prove or disprove.

This is the recurring theme of Rosslyn Chapel whose story is filled with a peculiar collection of puzzling tales.

(Birdsong) The chapel was built as a place of worship for the St. Clair family, who had built a castle on Rosslyn Estate in 1504.

The castle, as well as being a place of defense, was a scriptorium, literally meaning a place for writing.

Manuscript writing was a laborious process that could damage one's health, one prior complained in the 10th century.

In 1452, a fire in the castle consumed many priceless literary works.

Historical documents recount that during the fire, the Earl was in consternation as he raced from his bed to try and save his valuable manuscripts.'

There's a famous legend where he had three ladies-in-waiting and his wife, he raced past them through the fire to get to the books, and he threw two chests out the window as his servants were escorting his family out.

So, there were some seriously valuable papers and books and could they be under the church?

Yes, indeed they could.

However, I like to think they're underneath the castle.

That's where the scriptorium was.

I think that was what was thought, that it was the castle and there was a fire at the castle and the books were saved, but I don't know where they've gone now.

That may be the treasure.

I mean, there are all sorts of ideas.

'For a building steeped in the turbulent history of Scotland, ever since it was first constructed, it comes as no surprise that royal visitors came a-calling.

One royal visit in 1546, by Mary of Guise, wife of King James V and mother to the child who would become Mary, Queen of Scots, is inspiration for yet more fevered speculation about the chapel somehow being more than the sum of its pretty parts.

Following Mary's visit, she graced her host, William St. Clair, with a letter of thanks that included one enigmatic line, whose interpretation has been the source of countless theories.

She wrote, "We bind us and oblige us to the said Sir William and shall be a loyal and true mistress to him.

His Counsel and his secret shown to us, we shall keep secret."'

Whatever was shown to her was important enough for her to actually say this to him and to actually write to him, and the way the letter is couched, it's almost reverential.

I mean, this is one of the most powerful royal ladies in history.

I truly believe myself that the knowledge that was given to Mary of Guise, was knowledge of where Rosslyn was located.

There was an enormous push at that time to get to the New World, to get to America.

The Norse Vikings or the Norse navigators, the heritage of the St. Clairs who were from Norway, were navigators, and navigating over to the Eastern Seaboard of America from the 10th century.

I believe there's a map, a certain carved chart in the crypt of Rosslyn Chapel, and using that chart, you can teach a navigator how to sail to the Eastern Seaboard of America and back again using a prime meridian.

The temptation is to talk about the Rose Line that appeared in The Da Vinci Code.

He took that from a navigational line.

If you look at every nation in the world, they all have a prime meridian, to measure the landscapes and to create charts from.

Nobody yet has asked the question, "Where's Scotland's prime meridian?"

I believe he showed her a map, told her about the prime meridian that goes from Rosslyn Chapel, right over Arthur's Seat to the St. Clair castles and the fortification in Orkney, covering the longest piece of land mass on our nation and, with that knowledge, with a way to zero and calibrate your sea compasses, he passed on to the Stuart dynasty a way of sailing into that big unknown west and coming home again.

It's the secret of navigation and how to do it.

'Whatever the secret, the chapel has been the academic domain of just a handful of scholars for over six centuries.

But that was all to change in 2003 when author Dan Brown penned The Da Vinci Code and overnight, put Rosslyn Chapel on the world map.'

Well, it's been a really big moment in the chapel's history, actually.

It's had a huge impact for us and it's really sort of put us on the map, and it was very good timing for us, because, you know, as I say, when I first came here, we knew that something needed to be done.

And, of course, what it's done is it's brought the chapel out there so that people know about it.

Many more people come now than they ever did before.

And of course, everybody who comes, helps in its upkeep.

So really it's been a very good thing.

I think he's been very good for the chapel.

I have no problems with Dan Brown.

I think he's a novelist, he tells a great tale.

No, I have no problem with Dan Brown.

And, it's brought my home village and the chapel in my home village... a lot of work for local people and there's nothing wrong with that.

There's a wall that runs up the center, east to west, and opens out into arched chambers.

I think Dan Brown's research and the books that he tapped into to compose The Da Vinci Code story, you know, there's a lot of controversy out there over these books for years and he's taken the best of the best, the best of the worst and best criticized books, and put them all together into a genius piece of work.

You know, it's just another example of how it's been an inspiration to writers, poets, painters, whatever.

But I always think it's rather nice in the chapel's long history because it goes in cycles and about 200 years before Dan Brown wrote his book, Sir Walter Scott wrote a book which had the same sort of effect at the beginning of the 19th century.

So, you know, it goes in waves.

(RITCHIE) It got so busy that it became unhandleable.

I mean, I've been in the chapel at the height of the Dan Brown thing and there was over a thousand people coming in in an afternoon.

I mean, I've been elbowed in the ribs, pushed out of the way by small Spanish ladies wondering what I was looking at, because I was spending too much time looking at something through an eyeglass.

When I was there 12 years ago, 15 years ago, for the first time, there was a river running through Rosslyn.

The doors were hanging off.

It was virtually on its knees.

People just weren't going in there and so where would Rosslyn be today if it wasn't for Dan Brown?

It could be on its last legs.

It certainly was heading that way.

'Conspiracy theories involving a Holy Grail embodied by a beautiful descendant of the marriage between Christ and Mary Magdalene was the thread that ran through Dan Brown's best-selling book.

To say that Jesus Christ was married and had a seed, and that exists today.

I've done some math on this thing with the clan St. Clair over the last few years, and if that was the case, working on 2.4 children per generation, there's 21 and a half million relations of Jesus Christ alive today.

'The book and the film went global and brought people to Rosslyn in their hundreds of thousands, which in turn enabled the Rosslyns to carry out major restoration.

Although the restoration had begun before the film's release, it went into overdrive the moment Tom Hanks and Audrey Tautou walked into the sacristy at Rosslyn Chapel.

In 1995, reports confirmed that damage was being caused to the church by incoming water and high humidity.

In March 1997, a freestanding steel structure was erected to cover the chapel in an effort to help the stonework dry out naturally.

At this point, external stonework and windows began to be worked on.

Over the 16 years of restoration and conservation, thousands of man-hours was worked by scores of teams.

The cost of the stonework, stained glass window conservation, the organ restoration, landscaping and designing the building of the visitors' center came in at a staggering £12.5 million.

In the summer of 2013, the project was complete and for the first time since the conservation, our cameras were allowed to feast on the chapel's splendor.

Filming images not seen in such detail for well over a hundred years.

Nic Boyes was the stonemason who led the conservation.'

Just very recently as we were coming to the end of our project and we've got rid of the scaffolding, we're reminded just how beautiful the building is.

It's once again, standing in its own silhouette.

It's standing in its own space.

It's not being overlooked by anything.

And, you know, it's a real joy to be able to see that again.

'The window portals were built into the chapel in the 15th century.

The glass was not added until much later.

In 1736, Sir James St. Clair glazed the windows with plain glass.

In 1869, the Fourth Earl of Rosslyn added the first stained glass.

And in 1954, more stained glass was added.

Mark Bambrough and his team were tasked with the delicate job of restoring all 32 of them.

This is more a conservation than a restoration.

There were elements of restoration in that we're bringing back detail, legibility to the windows.

But the vast majority of the windows are being conserved.

The sense of daylight that must have been pouring through that building would have been extreme.

Because, it must be remembered that the original building had no stained glass.

The school of thought is that they probably ran out of money.

But the fabric of the building was designed to contain stained glass.

All the details, all the masonry details exist within all the openings to put in stained glass windows.

Imagine the building without stained glass.

It would look a very, very different... You would have a very different experience.

It needs that sense of gloom within the building, to create the sense of atmosphere, and the windows do that beautifully.

One of the areas of research I've been most involved with has been the east window.

But what I find very, very interesting is that... the scheme, the whole glazing scheme within Rosslyn Chapel, is fairly standard.

It follows traditional High Church arrangements.

You have saints with canopies.

You have subject matters with canopies.

These are all very traditional High Church gothic revival styles.

But what you have in the east window is very, very different in its iconographic form.

It portrays the visitation of the tomb.

The idea of Christ coming from the tomb.

But what's more interesting is that the main subject within this east window, isn't Christ rising from the tomb, it's the three Marys, and the central image of the three Marys is Mary Magdalene.

When we first came here, I came here about 30 years ago before we were married.

And it was... there was water running down the walls, and the ceiling was completely green with moss.

So, you know, you did feel that this poor building needed to be looked after.

So, it's been a long project but I think we've got there.

So there is a huge love for the building and a huge sense that we've got to hand it on to the next generation, so that a whole lot of new people can be inspired by it.

I just wanna take a look at the architecture and learn a little bit about the history.

I don't know anything about it.

I'm kind of coming into it without a lot of knowledge going into it, so just kind of hoping to get the feel for it when I'm inside.

Well, I read The Da Vinci Code and I saw the movie, so I just wanted to see it in person.

I haven't read The Da Vinci Code.

I know it's part of The Da Vinci Code but I have not read them.

But...that's the only place I've heard of it.

I think it will be interesting to hear... what's in there and just find out more information.

Most of what I know about it is from The Da Vinci Code, the Holy Grail, that sort of thing.

So, Freemasons, yeah.

'While it helped ensure Rosslyn's financial security for decades to come, Dan Brown's fanciful tale sent the conspiracy theorists into overdrive.

Stories based on shaky snippets of mis-matched facts, facts bent, cajoled and blended together to fashion a suitably bizarre narrative that captured the fevered imaginations of millions of escapist adventure fans.

Central to The Da Vinci Code is the theory that the Knights Templar, an organization set up in 1120 in Jerusalem, to protect pilgrim routes to the Holy Land, brought to Rosslyn Chapel a treasure of unimaginable distinction.

Lost religious scrolls from the time of Christ.

A piece of the Holyrood, the cross upon which Christ perished.

Or even Christ's embalmed head, are just a few of the things said to have been safely secreted by the Knights Templar seven centuries ago within a secret chamber in Rosslyn Chapel.

The Knights were war machines turned financial wheeler-dealers who bent the rules of their Christian faith to make vast fortunes from money-lending.

Christian European rulers paid handsome homage to the Knights Templar in the form of money and prime land holdings.

But did that include the St. Clairs, and were the Knights Templar ever at Rosslyn Chapel?'

(LADY ROSSLYN) Well, who knows?

It's very difficult to tell about all these things, isn't it?

There are certain theories that they were and that there are links between the St. Clair family and the Knights Templars.

And there are certain theories that the Knights Templars' treasure is here.

But, as I say, I think the important thing is preserving the building and preserving the mysteries and the myths.

The Knights Templars' main logo, their symbol was two knights on one horse.

Two knights on one horse represented poverty of the Knights Templar, so, historians come along post-Da Vinci Code and see two characters on one horse, what else is it?

It's the Knights Templar logo.

It's Queen Margaret being taken back to Scotland by William St. Clair.

It's a child on the back of a horse with a cross.

Now we know in history that in the 11th century, Queen Margaret was escorted back to Edinburgh by William St. Clair of Rosslyn.

She gave him the estates, the barony of Rosslyn in return.

What did she bring with her?

A part of the cross of Christ, the Holyrood.

'So what of the legend of the 12 Knights Templar buried in their full armor underneath the chapel floor, ever ready for the moment they must rise to defend the hidden treasure of Rosslyn Chapel.

There are probably knights down there in their armor, but, of course, don't forget that Scottish families would have buried their own members of their family under there.

So they may well be Scottish knights.

They may well be Scottish St. Clair knights.

There were most definitely knights under Rosslyn.

There were...

I think Sir Walter Scott talked about the knights in their armor with all their weaponry around them.

Now there's lots of historical evidence to suggest that they were there.

What's wrong with a Scottish knight?

That's what was underneath Rosslyn in my eyes.

I kind of think the Knights Templars undermine the Scottish knight system and that whole thing.

It kind of gets rid of the glory that somebody's achieved in real terms, fighting for Scotland in the wars of independence with England.

Every time I look, I see another face.

It looks as if you're always seeing different things.

And, of course, there's so many ways to interpret... 'Ian Gardner is the director of Rosslyn Chapel.'

Of course, the acoustics are great.

They really lend themselves to recitals and concerts.

In fact, we've got a group coming in from Heriot Watt University to sing for us, - so I think that... - Lovely.

..will sound great in such a good setting.

Yes, it will.

'For decades, art history scholar Lady Helen has cast her eye over the thousands of stone artworks crafted centuries ago by stonemasons of a bygone era.

She may well be able to discuss miniature statuary with the familiarity of a devotee owner, but the one thing she is always conscious of is the privilege that this position affords her.

She may well have spent more time dwelling upon the carvings than any other living scholar.

But even she admits to having favorites.'

This is a really magical carving because it's the whole of the Nativity story.

You've got the star-of-Bethlehem at the bottom, and then, going round, you've got all the figures associated with the Nativity.

So you've got Mary and Baby Jesus.

You've got the manger, Joseph and the kings and the shepherds.

But what makes it even more special is the fact that all these angels here, are watching the Nativity scene.

So you've got all these angels with their musical instruments: a medieval shawm, a pipe.

And there's the bagpipes, the angel with the bagpipes, which is rather amusing.

But, even better than the angels on their own, if you look very closely, you can see that between the angels, you've got the Green Men.

And that happens in between each of the angels.

There's a little Green Man peering out from the foliage.

And that's really lovely, because it's what this chapel is all about.

It's the mixture of the religious symbols and the pagan symbols.

It's really bringing all those images from the rural fields into the chapel.

Now that's extraordinary because that carving is supposed to be an elephant.

Now, why is there an elephant here in Scotland?

There are lots and lots of different animals all around the building and that, it is quite amazing.

One of the really special things is that, if you think about it, in the 15th century a lot of people couldn't read.

So actually, quite a lot of moral stories are incorporated into the carvings, and this one here, this is a great example of telling moral tales in stone.

This one is the Seven Virtues or Corporal Acts of Mercy.

And it's rather lovely because each of the stones up there has got two figures, one helping another.

And so, from the left, it's helping the needy, clothing the naked, visiting the sick and visiting those in prison.

And can you see that face behind the bars in the prison?

And then you have two figures, feeding the hungry, burying the dead.

And there is St. Peter at the gates of Heaven.

This is a really intriguing carving because, if you look at it, it's actually Native American corn, and at the time the chapel was built, there was no plant like it over here.

So, there is a theory that Prince Henry St. Clair, the grandfather of the chapel's founder, actually discovered America a hundred years before Christopher Columbus.

And that it was his knowledge that gave them the information to carve that.

So, it's an interesting theory.

And here's another carving that's quite intriguing.

It's the Veil of Veronica.

The story where Christ was handed a piece of cloth by a lady and wiped it over his face and an image of his face came off on the cloth.

And there you can see the image of his face really clearly.

Now why that's there in amongst all the other carvings, who knows?

It's just another mystery, but it's very clearly carved.

And that's really what's magical about the whole building actually.

It's the mixture of the plant imagery, and the religious imagery.

And you've got this string course that runs all the way around the chapel under the windows, and suddenly, in the middle of it, you'll have a Green Man face.

So you get this sense that there was a whole team of stonemasons working together and they were all doing their own bit.

One was carving over there and one was working over here on something different.

A really important moral tale that would tell people how to live their lives.

The chapel's often been called the Bible in stone.

So it's rather lovely to see all these angels dotted around the chapel telling the story.

And that one, has got a closed book and it's as though it's the end of the story.

And in fact, traditionally, the Bible story does start in the east end of the chapel and so that would be the right place for the end of the story.

'A chapel studded with legends from the religiously sublime to the sci-fi ridiculous, naturally draws some visitors who tend to dwell on the eccentric side of the tracks.

Guido Viaene and his band of New Age ley line evangelists have spent 18 hours traveling 624 miles from their home in Antwerp, Belgium, in an attempt to discover the rhythms of energy running through Rosslyn Chapel.'

Here.

So this is an underwater flow.

- Radiation zone.

- Yes.

Under this chapel, yeah, this is the first, that we determine.

We will look if there is a second.

'Some believe that ley lines, vortex and earth rays are energy sources that were considered holy.'

There is a second one crossing here.

We got earth rays in one direction and you have opposite direction, also earth rays.

So there are two earth rays crossing this building in this way, and maybe there is also another crossing in the length of the building.

That's why we will start there and go in this direction.

(Chatter) (Laughter) Another one here.

- Here.

- Yeah.

So, parallel with the earth ray under the chapel in the length...

There is also one here.

You will see at the inside, that on the cross of two earth rays there will always be there the most...religious objects.

(Low chatter) Normally this earth ray should be found in the middle but it's next to the middle.

So it's strange, it's not normal for a construction of a chapel.

We still have to visit the crypt, and there, maybe, there will be a lot more to be felt, but this is a special place.

It's a place of mystery.

We feel that there is a special energy here.

This is, in fact, a book, a book in stone.

People who are joining Freemasonry, they know what it means and by seeing the details, they can reconstruct the whole secrets, knowledge, which is hidden in this area.

Everybody's fantasies about the place are valid, for them, and that's lovely.

Really, what we're trying to do is maintain the fabric of the building so that people can be inspired in their own way.

And I think that's right.

If somebody comes in here wanting to see whatever they might want to see, they can't help but be captured by the magical atmosphere of the place.

It's a special energy.

Look, just across the door, and what we have found.

Look on the wall.

A lot of Freemason symbols like this.

'Freemasonry is a fraternal organization that can trace itself back to late medieval stonemasonry and some believe even further to Solomon's Temple.'

If I took a Freemason to Rosslyn Chapel tomorrow and said, "Point me out one single Freemasonic, definitively Freemasonic symbol," he's gonna look at me and have a search.

And he's gonna smile and go, "Aye, you're right."

There's not one that's definitively Freemasonic.

There's lots that can be interpreted.

Yes, yes, interpretation is...

This has to do with the symbolic message of the Freemasons.

This is what they have put on the wall.

Freemasons didn't exist when Rosslyn Chapel was built.

Here behind, there is something special.

To be found, I'm sure.

Yes.

This is something special here.

When they hide things, it will be hidden here under.

Yes, yes, yes, because this is the power of the earth.

I know for a fact there's something underneath it.

I mean, it's like every other 15th-century church that I've worked in.

There are inevitably sub-floor burial chambers and so, yeah, there's nothing unfamiliar about that.

I think there's more than one space.

I think the church probably goes down two or three levels.

I've worked on projects in the Gardener's Brae in the south side of Rosslyn Chapel.

I've seen poles being pushed into a tunnel from the south door to the castle between the church and the castle.

I've seen a 23-foot metal pole being pushed into a hole and continuing and sliding and going.

There are tunnels for sure, tunnel systems.

Most castles and churches had tunnels, escape tunnels if nothing else.

But there's spaces under there.

I don't know if there's a room or not.

I like to think there's a room under there.

The last proper scan that was done at the excavation was pushing a tube, a plastic pipe through, down through the grave that was lifted and into this hole.

But every time the camera was fed through, sand would come in.

And back there, ten years ago, I was tempted to think, "That's by design, you know.

Indiana Jones traps and all that.

Where's the snake pit?"

But, no, there's definitely spaces, but no one's been in to see what's in there.

And I must say as well, as dry as I'm being, basing everything I see on evidence, the subjective evidence to suggest that something lies underneath Rosslyn Chapel is huge and it can't be just discounted.

There are so many theories and stories, which it's very hard for us to prove or disprove conclusively, so people can come in with all sorts of ideas about how the building has come to be as it is today, what some of the carvings mean, how they can be interpreted.

And then somebody can come in ten minutes later and completely disagree with that and have their own version.

But for us, it's a really...

I think it's great that in some ways there are no right or wrong answers.

I find Rosslyn like an onion.

Because you peel back one layer, there's another one.

You think you've cracked it and there's another layer.

And I don't know where all these myths and legends come from but there's no smoke without fire.

Something started it off.

And it could be simply because we don't know much about medieval life.

You know, times back then, and we don't have any of the original plans.

So it lets people just attach things onto here and you've no way to prove yes or no.

Which makes it more interesting.

'Guide Anne McNeil has seen all sorts come through the door at Rosslyn Chapel, although some don't use the door.'

A lady comes in and tells us that Elvis is buried in the chapel.

The lady came through a portal from Memphis, Tennessee.

She followed Elvis.

The next day someone will come in and say, "Where's Elvis?"

So, it's instant, things like that.

Oh, yes, we were... it was the end of the world, the Mayans.

So we got, "This is a Mayan temple now."

And they all came down the lane with the bells and everything, and they all came in here because they thought that the world was going to end.

But fortunately, they walked away again.

We don't say that things are right or wrong.

We give stories as we think we can best explain them.

Other visitors will have their interpretations.

To me, that's an ideal, because it keeps the debate going.

It keeps the intrigue going about Rosslyn Chapel.

'Another intriguing theory is that the chapel was constructed to look like a church in order to escape censure from higher authorities in Rome and that its real purpose was an astronomical observatory.'

You could say all churches were astronomical observatories.

They were built to record time and the passing of time, to establish Easter.

The race to establish the true date for Easter.

That was done with the pillars and light.

But I think there was an astronomical observatory right there on Rosslyn Hill 300 years before the church was built.

'Theories and conspiracies go hand-in-hand at Rosslyn Chapel, generating much debate and there can be no doubt at all that thanks to Dan Brown millions have now joined in that debate.

Pre-Da Vinci Code, the chapel was visited by a handful of visitors a year.

After the book was released in 2003, Rosslyn began to play host to over 30,000 visitors every month.

Who, like Brown's main character Professor Langdon, wanted to enter the mad house of mysterious carvings and stare at the crowded walls and tick off Christian, Jewish, Egyptian, Masonic and Pagan influences.'

The overwhelming symbolism is not what I expected whatsoever.

I didn't have any idea of how ornate this would be and how you could literally spend days in here and just staring at absolutely everything.

It's amazing.

It's incredible.

It's so detailed.

Every last piece of it has something to look at.

There's just not enough time in the world probably to take it all in.

I was very surprised to see everything that was in here.

I didn't know it had so much artwork and symbolism within the chapel.

Every single thing you look at can be interpreted differently.

I see that.

I see different things than my friends see, and they see different things that I see.

Because everything is laid out the way that it is, you can tell that there is a reason for it and there is a specific pattern and trying to figure that out is really the amazing part of it.

I think you can walk away with your own interpretation.

We may not know why the carvings are here or some of the things they put here.

We can walk away with whatever perception we want to have.

But it's very intriguing to try to think about why this was placed here, why this was created.

I've never seen anything like it in my life.

It's like nothing that I've ever seen.

I'm from America and I'm from the west coast of America, which is the newest part.

We have nothing really made of stone, and nothing even remotely resembling this type of workmanship.

The detail on just things that would be made of stucco and brick is fantastic.

I've never seen anything like it.

Ah... Amazing!

There's just so much in it for such a small building.

I've seen all the big cathedrals that you can think of - St. Paul's and so on.

They're magnificent but they're nothing like the intricacy that you can find in here.

The chapel itself is just absolutely fantastic.

We were coming up and they were saying, "It's six, seven hundred years old."

I was telling everyone else: that's twice as old as our country and it's in much better shape.

I spent most of my time in awe.

The detail, searching out all of the nooks and crannies that they were telling us about.

And the fact that it is so old, that the stone is wearing away, just boggles my mind.

So, I love it to death.

'Mindboggling, it might be.

But... what is the Rosslyn treasure?'

I love the fact everybody has their own idea about what the treasure is.

That's wonderful.

But for me, this is definitely the treasure.

The treasure is the building.

I mean, this really is such a treasure.

Where else do you see this much 15th-century carving... in one place?

The real treasure is in the carvings because so far, we've been able to actually connect them to about eight different manuscripts that were extant at the time the chapel was being built.

And these were carved into the wall for a good reason, in order to convey the whole religious philosophy at the time, which wasn't Catholic.

See, when you hear that for the first time, it's quite warming of heart.

Can I be honest?

It's become a cliche when people say that to me - "The building is the treasure itself."

Let's look beyond the stones.

Let's look beyond the myths and the legends.

Let's get to try and understand the blisters and the hands of the builders who built the thing.

Let's look at the social infrastructure that surrounded Rosslyn.

The people: How did they live?

What were they paid?

What did they know?

What did they sacrifice?

And that can all be told by looking closely at the building.

The evidence and the fingerprints of our past are on the rocks and the stones surrounding Rosslyn Chapel.

Just thinking about the people who made all of this.

All of this beautiful work for our pleasure today.

We're just passing it on to the next generation.

We're effectively standing in the footsteps of the people who originally built this building.

Each individual carver in doing the work they were doing here, they were communicating.

They weren't necessarily communicating with us but they were communicating with God, for example.

They were looking after their souls.

What that mason carving 550 years ago wouldn't have expected, I think, was for me now, to be looking at the same carved stones and to be hearing the clear message that he was sending at the time of carving it.

(LADY ROSSLYN) We don't have any names.

I think that is what is so extraordinary.

This wonderful building, it's such a work of art.

But they didn't leave their names, they left their masons' marks, which is purely really a stamp so that they could be paid for their work.

And...

But we don't have any names.

We don't even have the name of the master mason.

And that really is quite extraordinary.

But you get a lovely sense of this team of masons that traveled from one building to another.

Each with their own particular skill.

There was probably somebody who was particular skilled in botanical carving.

Somebody who was particularly skilled in Green Man carving.

And they've all come together here and they've all done their bit.

'And so, this quaint place of worship, dating back more than half a millennium finds itself forever associated with compelling strange myths, unlikely legends and questionable conspiracy theories attracting endless debates.

It could possibly be home to the Holy Grail, to the skull of St. Matthew or John the Baptist or even Jesus Christ himself.

Its walls and pillars and secret underground chambers might hide untold fortunes in jewels or religious scriptures dating back to the time of Christ.

Or, it might play home to 12 knights in armor patiently awaiting the call to rise up and save the chapel in its hour of need.

It may even sit atop a spaceship from a faraway galaxy.

But the truth might be a lot simpler and closer to home.

Many believe that the chapel, famous for its vast and curious array of stone carvings and statues, was quite simply a school for stonemasons.'

If you get to know Rosslyn intimately, it's actually quite crude.

Some of the faces, some of the Green Men, they haven't been built by the hands of masters.

They've been built by the hands of hundreds of apprentices.

It was a teaching school for modern stonemasonry in Scotland.

It encapsulates thousands of years of building heritage in Scotland.

It's not something that happened, it's something that developed.

And that's what Rosslyn is, something that developed for the builders' hands and the architects' minds of Scottish stonemasons.

And Rosslyn arrived after thousands of years of development through time.

# In the still of the night # As I gaze from my window # At the moon in its flight # My thoughts all stray to you # Stray to you # In the still of the... What one word would I use to summarize Rosslyn Chapel?

Disappointed.

# ..is in slumber # All the times without number...

I think that's the word Rosslyn Chapel would use to summarize its own position just now.

I think if it was a living, breathing entity it would go, "What's happened to me?"

(Choir continue singing) That's interesting, one word.

Intriguing.

# ..as I love you # Are you my life to be # My dream come true...

Magnificent!

# Or will this dream of mine # Fade... Home!

# Like the moon growing dim # On the rim...

It's difficult to pick a word but probably "timeless", because every generation sees something different in it.

So I suppose, yes, timeless.

# Of the night # The still of the night # There is nowhere in Scotland, arguably the world, as special as Rosslyn Chapel.

To learn more about Great Estates, visit pbs.org Great Estates of Scotland is available on DVD.'