The Trylon and Perisphere were two monumental modernistic structures designed by architects Wallace Harrison and J. Andre Fouilhoux that were together known as the Theme Center of the 1939 New York World's Fair at Flushing Meadows–Corona Park in Queens, New York City, United States. The Perisphere was a tremendous sphere, 180 feet (55 m) in diameter, connected to the 610-foot (190 m) spire-shaped Trylon by what was at the time the world's longest escalator. The Perisphere housed a diorama by Henry Dreyfuss called Democracity which, in keeping with the fair's theme "The World of Tomorrow", depicted a utopian city-of-the-future. The interior display was viewed from above on a moving sidewalk, while a multi-image slide presentation was projected on the dome of the sphere. After exiting the Perisphere, visitors descended to ground level on the third element of the Theme Center, the Helicline, a 950-foot-long (290 m) spiral ramp that partially encircled the Perisphere.