Hidden beneath the streets of London is a secret subway that only carried mail.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

2 square block factory in Greenpoint erected in 1936.

A dark, dank room in subterranean Manhattan was the site of a ghastly murder.

The site of the deadly Triangle Shirtwaist Factory Fire.

A modern addition to the Greenpoint skyline.

A 9-story, poured concrete structure which was used as a glue factory with an indelible smell.

This 19th century brick building in Brooklyn stands out like the anachronistic landmark that it is.

A drawbridge named for a potentially intersex Polish national who fought alongside George Washington during the American Revolution, and an example of "Pulaski Red".

A Pythagorean funhouse that tries, successfully, to prove that math is the coolest thing ever.

A Bed-Stuy gymnasium that hosts expansive raves, performances, dance parties, and more.

A whimsical, but often overlooked clock in Park Avenue.

A working metal shop and venue for outrageous art and music shows in a former cannonball factory.

Keshwa chaca, among the last handwoven Incan bridges, crosses Apurimac Canyon in Peru.

A Manhattan office building is home to the world's largest chess board.

Walk into the 19th century without leaving Brooklyn.

Check out the underground party scene at the "Burning Man of Brooklyn."

This innocent-looking townhome is actually a subway exit.

Detailed facade of a brownstone in Boerum Hill.

Prove you deserve to be fed by Kenny Shopsin.

An illegally built ramshackle mansion tucked in the middle of Brooklyn is now being turned into condominiums.

Behind a bodega is a small museum of relics and ephemera showcasing the history of New York.

Abandoned power station once home to a squatter community, now being developed into an arts center.

A tiny museum housed in a New York freight elevator specializes in the "overlooked, dismissed, or ignored."