The only structure left with direct ties to the Salem witchcraft trials of 1692.

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.

Remants of foundations, streets, and streetcar tracks inhabit the cliffs where a landslide occurred in 1929.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

This beautiful building in the heart of Manhattan's Financial District was empty for decades.

These fantastically named natural pools look like something out of a Scottish myth.

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.

A historic 1890s architectural masterpiece with an iconic clock tower that, once open to the public, now faces an uncertain future.

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

A crumbling hospital from the 1850s on Roosevelt Island.

World's first "penitentiary," meant to be humane, drove men insane.

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

Rippling sand dunes frozen in the Arizona rock.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

During prohibition, corrupt city officials ran drinking dens under the streets of Downtown Los Angeles.

A huge musical instrument played by the ocean.

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

The purported world's shortest international bridge connects a homeowner in Canada to his backyard in New York.