#1 Abandoned hospital on North Brother Island, a small island in the East River, between Queens and the Bronx
In 1950, Riverside Hospital was moved to this island in order to isolate patients with smallpox. Soon after, it expanded to include patients with other diseases which needed to be quarantined. The hospital closed in the late 1930s, and the island was used for other purposes. Because of a housing shortage after WWII, war veterans attending nearby colleges lived on the island. In the 1950s, the island housed a treatment center for adolescent addicts. The treatment center closed in the early 1960s, and the island is currently a bird sanctuary.
Image credit: en.wikipedia.org