This abandoned structure, originally covered by an enormous, multi-colored, translucent suspended roof, was part of the New York State Pavilion at the 1964-65 World's Fair. Inside, sprawling across the floor, is a 130-by-166-foot terrazzo road map of New York State, heavily deteriorated after decades of neglect. It's currently hidden from view, however; in 2009, it was covered by protective layers of sand, geotextiles, and gravel in an attempt to preserve what's left of it. You can see a photo of the map in all its World's Fair glory here, and you can also spot it on several occasions in the circa-1987 music video for "Don't Let's Start" by They Might Be Giants, which was mostly filmed inside the Tent.
Flushing Meadows Park was the site of not only the 1964-65 World's Fair, but also its 1939-40 predecessor. Before that, however, the park wasn't a park at all, but rather a vast ash dump run by a Tammany crony named Fishhooks McCarthy. This befouled landscape was immortalized in the pages of The Great Gatsby:
About half way between West Egg and New York the motor road hastily joins the railroad and runs beside it for a quarter of a mile, so as to shrink away from a certain desolate area of land. This is a valley of ashes — a fantastic farm where ashes grow like wheat into ridges and hills and grotesque gardens, where ashes take the forms of houses and chimneys and rising smoke and finally, with a transcendent effort, of men who move dimly and already crumbling through the powdery air. Occasionally, a line of gray cars crawls along an invisible track, gives out a ghastly creak, and comes to rest, and immediately the ash-gray men swarm up with leaden spades and stir up an impenetrable cloud, which screens their obscure operations from your sight.Realizing that a tremendous amount of money would be required to convert the old dump into parkland, Robert Moses seized on the idea of holding a World's Fair here in 1939, using the financial resources available for the fair to level the ash mounds, dig out lakes, and lay down topsoil, turning what Moses described as "a cloud of smoke by day and a pillar of fire by night" into one of the largest parks in New York City.