he Guggenheim design mimics an upside-down ziggurat consisting of a large, top-lit interior court ringed by a continuous spiral ramp. The dense mass of the ramp and exterior walls separates the interior world of the museum from the city’s streets, creating a contemplative environment for viewing art. Visitors take an elevator to the top of the museum and slowly descend its spiral gallery. Wright was roundly criticized for the awkward exhibition spaces of the Guggenheim, whose curved walls and sloped floor defy conventional display techniques. The structure takes the cantilevered concrete floor of Wright’s earlier projects (for example, Fallingwater and the S.C. Johnson & Son, Inc. Research Laboratory Tower) and twists it around a central court. Indirect light enters the building through narrow windows which, on the exterior, separate the ramp’s levels. Negotiations with building department officials, shortages of materials and changes in the museum’s administration all delayed the beginning of construction until 1956. It was completed in 1959, six months after Wright’s death.