The smallest island in Manhattan is a manmade landfill dominated by a Buddhist peace arch.

The greatest real estate coup of all time.

Constructed in the 1920s, this former pencil factory is now an office building.

HBO series' stage tucked away in a Greenpoint lot is the largest theatrical set of its kind in the United States.

The home of aviation trailblazers, in a remote corner of the big city.

A young woman's senseless murder led to the controversial psychological theory of the "bystander effect."

An unconventional space for art and science housed in a massive old warehouse.

Failed state-supported institution meant to rehabilitate students with intellectual disabilities.

This mysterious marker puzzles pedestrians and infuriates geographers.

A remnant from the golden age of aviation still in use today, Pan Am's Clipper service took off from this Art Deco gem.

The last living thing to come out of the rubble after 9/11 is now a symbol of hope and resilience.

A retired subway car stands alone in a field in the middle of Queens.

A once crucial portion of the Long Island railroad still lays abandoned, waiting to be turned into an urban park.

Walk into the 19th century without leaving Brooklyn.

Empty, but not abandoned, this cavernous Brooklyn loading dock was once considered the largest individual building in the world.

This otherwise innocuous bodega was once the headquarters of the most feared assassin's guild in American history.

The most unloved grain elevator in Brooklyn was a “Magnificent Mistake.”

The mass grave of a heroic Revolutionary War regiment sits below an empty lot near the Gowanus Canal.

The one-time epicenter of American songwriting is now a little remembered Manhattan commercial block.

Dodge prohibitionists and slide through the telephone booth in Crif Dogs.

A 140-year-old castle with underground caves hidden in San Francisco.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

Bring your own cardboard to the slippery slopes of concrete hidden in a neighborhood park.

An artsy hidden staircase leads to breathtaking views of San Francisco.