There's the New York City you know, and then there's the New York City you don't—miles of forbidden sites sealed off from the general public, languishing behind closed doors or chain link fences punctuated with WARNING signs.

During Open House New York, the locks come down, affording the public behind-the-scenes access to hundreds of the city's cordoned-off treasures. A full list won't be available until October 6, but a press release touts a tour of the 200-year-old City Hall and a peek at Google's Chelsea headquarters. In years past, amateur explorers have kicked back at JFK's classy as hell TWA terminal, roamed the five million square-foot Brooklyn Army Terminal, and marveled at 4,400-square-foot superdesk found in one chummy Manhattan office.

OHNY will be held the weekend of October 17 and 18. Though most sites are open access and can be visited without reservations, some require tickets. Secure your spot starting on Wednesday, October 7 beginning at 11 a.m. by following this link. Be advised that the hottest tickets sell out pretty much immediately, so don't sleep on this.