(wind whistling) - [Jessica] We're going to go up the Clackamas River and get some caches.

We've been meaning to go up there for a while.

- [Narrator] It's treasure hunting day for the Dhone family.

Today they'll hunt along a river.

Climb up into a small cave.

- [Bruce] It's probably either going to be under a rock or in a hole.

- [Narrator] And search the forest floor.

- I don't know.

I can't really see good right here.

- [Narrator] Secret stashes invite players into a game that has swept the globe.

- [Bruce] Found it!

- [Narrator] They call it geocaching.

- [Jessica] Go look around that one.

- [Narrator] Jessica Dhone is out with her sons, Bruce and Nash, and their father, Kevin.

They hope to find 10 hidden treasure sites, or caches, today.

- It says, "With three giants, this one sleeps."

- [Narrator] They looked up hints on the computer before they left home.

Now they get guidance from geosynchronous satellites in outer space.

- 4-85.

Now we're getting closer.

He memorizes the numbers and we follow the GPS to the right area.

- [Bruce] Yeah, it looks like it.

- It's cheap entertainment.

It's family friendly.

We get to go everywhere.

- [Bruce] And there's marbles in it.

- [Jessica] Is there?

- [Narrator] The Dhones are part of a worldwide phenomenon.

The leading geocaching website estimates two to 3 million people actively geocache.

In this treasure hunt, finding the prizes comes with one golden rule.

- If you take an item, you leave an item.

So that's the main thing.

And you need a trade.

- Yeah.

- You don't put in junk for something really nice.

- [Bruce] Yeah.

- What is this?

- They're tweezers.

- Oh.

- [Narrator] But there's no referee, no enforcer.

- We'll trade the sand dollar for the octopus.

- [Narrator] Just the honor system.

That, and whether you find anything you really like.

- [Jessica] And sometimes you don't trade at all.

- Yeah.

Sometimes they're pretty lame.

(Jessica laughs) - [Narrator] The trinkets people leave behind may be small, but folks must like them.

The geocaching website reveals hundreds hidden in just one Portland neighborhood.

Across the globe, there's now more than 800,000.

- We're less than a 10th of a mile from it.

That looks like it right there.

- [Narrator] Jim Meisner is known as P-D-X Jim in geocache circles.

He and his friend Kathy Suiter lead us to the site of the first ever geocache.

The very birthplace of this sport sits near Estacada, Oregon.

- And it started right here on May 3rd, 2000.

- [Narrator] Geocachers have set a memorial plaque here, and they stashed a new cache to keep tradition alive.

- [Jim] When I came here the first time, it was almost like a pilgrimage, 'cause this is where it started.

And it's kind of a neat feeling.

- We're looking for the unusual and the unique.

The problem with that is once we find it, we tend to want to share it with everyone.

- [Narrator] We met dozens of geocachers at a party celebrating the anniversary of this high-tech sport.

- We first discovered it just accidentally, and found places that we had never, ever would've seen had we not been taking hikes, looking for caches.

- Folks go to geocaching.com on their computer, find a cache that looks interesting to them.

Write down or download the coordinates, put them in their GPS and go find it.

- It's not just a cache, it's an adventure.

- I have a cache in my front yard so that I can meet geocachers.

- Underneath some branches.

- [Narrator] Sometimes the secret treasures aren't just for kids.

Adults leave items that can be tracked as people find them, move them and hide them, over and over again.

- [Jim] This number is its tracking number.

So you can see every cache it's been in, who's had it, and how long they kept it.

- [Narrator] That coin Jim kept ever so briefly started in Washington, traveled through Oregon, and was last spotted in Oklahoma.

Some coins take very long journeys.

The original owner can watch it every step of the way, because there's another accepted rule.

If you find a cache, you sign the paper in the cache, plus you log where you picked it up and which cache you moved it to on the public geocaching website.

- About five years ago, for example, we placed a travel bug in Perth, Australia, and it just came home a couple months ago, having traveled to Europe and the States and Canada and back to Europe, and as I say, almost four and a half, five years later, it returned home.

- [Jim] That looks like the trail.

- [Narrator] Jim Meisner is the Energizer Bunny of Oregon geocachers.

- And here it is.

Here it is, up here!

Yes!

- [Narrator] He's got a knack for finding them, big or small.

- [Jim] I found 37 last Saturday.

- [Narrator] Jim's found more than 7,800 caches so far.

This game also depends on the integrity and good judgment of its players.

- See that sign?

We don't trespass.

- [Narrator] There's an accepted etiquette in how people hunt.

- You don't want to destroy the vegetation, 'cause then people will get upset with people geocaching, and you won't be allowed to do it.

- [Kathy] Okay, we got that one.

Should we go to the next one?

- [Jim] Yes.

- [Narrator] It's a game that thrives because the people who play it keep creating new hiding places with more treasures, all over the world.

- And then you just put everything back and put it back where you found it.

And usually, you try to hide 'em better than when you found them, and that way they don't disappear.

Can you see any of it?

You're supposed to hide it well, remember.

- Okay, now you can't see it.

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