This month, Open House New York is unlocking the doors to some of the most interesting, beautiful, and closely-guarded structures in the city for one special weekend.

A legal and sanctioned urban exploration bonanza, the weekend features dozens of guided tours and events between October 15th and 16th. Some are completely open access, while others require reservations that always fill up fast, so set yourself an alert for tomorrow (Thursday) at 11 a.m. before reading any further if you're interested.

On the complete list of locations accessible during OHNY, gilded landmarks like the Woolworth Building and Alexander Hamilton U.S. Custom House stand on equal footing with weathered industrial spaces like the Brooklyn Army Terminal, which served as a supply depot during World War II and is currently inhabited by artists' studios. Some sites will feature special panel discussions.

You can peruse the full list of reservation-only sites below, but allow us to offer some of our favorites:

  • One hour tours of the Woolworth Building's landmarked lobby will include discussions of the building's architecture and construction.
  • A behind-the-scenes hard hat tour of the construction at Manhattan's Pier 17.
  • The lavish (and occasionally weird) National Arts Club in Gramercy will be open for 30 minute visits.
  • Check out one of three behind-the-scenes tours of the Metropolitan Opera.
  • Travel up to the city's Manhattan Municipal Building's rarely-accessible cupola, where you can enjoy 360 degree views of Lower Manhattan.
  • Peruse the New York Hall of Records inside Manhattan's Civic Center while guides fill you in on the facilities' architecture, history, and artwork.
  • Google's Chelsea offices will be open for tech and design-lovers itching to know what it's like to spend a day at the company.
  • The Department of Sanitation's Manhattan 11 Sanitation Garage in East Harlem is packed with "mongo"—the weird stuff that sometimes gets rescued out of the garbage. One retired DSNY worker has spent over 30 years maintaining the garage's assemblage of treasured trash, and he'll be around all weekend to talk about it.
  • The lush amenities and gorgeous rooftop of 170 Amsterdam, New York first high-rise built with an exposed diagrid structure, will be open.

And if you end up missing the reservation period, don't sweat it! There are still a multitude of great options in OHNY's roster of open access events, including trips inside Kings County Brewers Collective in Buswhick, the stunning Gil Hodges Community Garden in Gowanus, the Bronx's Gould Memorial Library, the art deco interior of LaGuardia Airport's disused Marine Air Terminal. Check out the full list of options here.