The world's oldest hologram gallery and the labyrinthine laser laboratory of a holography pioneer.

Built as a gift to the hottest tastemaker of the time, these hidden quarters remain an Art Deco showpiece.

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

Manhattan's Thirteenth Avenue was made on landfill then deliberately destroyed — apart from one small, obscure block.

A trove of century-old litho stones from the Puck Building's printing days were discovered behind a cellar wall, and are now hanging in the store.

Built hundreds of years ago this downtown iron barrier once protected a much despised king.

Walk into the 19th century without leaving Brooklyn.

Avoid gangster interaction while window-shopping.

An uber-secure, windowless tower of doom in the center of Manhattan is an NSA spyscraper.

Under a glass sidewalk lie the remains of some of Manhattan's oldest buildings.

One of the last few places in Manhattan that employed a pneumatic systemic keeps it on display.

Final resting place of Typhoid Mary.

A former connection to City Island, it has been abandoned since the 1930s.

Small monoliths of several varieties of stone sit alongside a wooded path in the Bronx.

Collect holy water from a Bronx grotto.

The oldest house in Manhattan is now a museum that remembers the home's sordid history of scandals, vice-presidents, and ghosts.

Harlem park dedicated to compulsive hoarders killed by their own junk.

This former sugarcane transport tunnel is now a portal to a lovely beach.

Rusting, graffiti-covered tanks litter the beach of this island, once used by the U.S. military for target practice.

The world's brightest bioluminescent bay.

On a small Puerto Rican island, banks of secret naval bunkers lie abandoned and filled with piles of office equipment.

This limestone cave offers an incredible view of the Río Grande de Arecibo valley.

The highest peak in Puerto Rico is home to a rare fern that can only be found on six trees at its summit.

This niche museum devoted to ancient religious artifacts is shaped like the very thing it displays.