That weird structure is the Parachute Jump at Coney Island, an amusement ride that opened at the 1939-1940 Worlds Fair and was moved to Coney from Flushing afterwards. (I wrote it about it: here.) In 1978, when the HAER survey of it was made, it had been abandoned for ten years and Coney Island itself was in rough shape. The old amusement parks had closed and not much had replaced them; after building a bunch of housing projects north of Surf Avenue, the city pretty much ignored the area for decades. Overgrown vacant lots, like the one in the foreground, were everywhere. The beach, of course, was still immensely popular.
Things have changed for the better since then, both for Coney Island and for the Parachute Jump. The ride is still closed, but it’s been fixed, painted, and has lighting at night.
This has been the set-up. Tomorrow’s post will be the payoff.