"NY77--The Coolest Year in Hell"
82 minute documentary about New York City in 1977. The documentary focuses on the new music of that year--punk, hip hop, and disco--but it's especially interesting concerning how bad off the city was then. Apparently, big cities in a lot of trouble can be saved.
(Some NSFW words and images--this was the heyday of Studio 54 and Plato's Retreat.)
See also the disturbing 1975 "Welcome to New York City" pamphlet.
You should never ride the subway for any reason whatsoever.