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

Dramatic river bend surrounds a natural red-rocked pedestal.

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

These old stone ruins in the Oregon wilderness were once bathrooms and are steeped in legends of murder.

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

An abandoned cemetery lies in ruins as the surrounding forest swallows it whole.

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

An emerald-green grotto just a short trip from Austin.

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.

An immersive environment that is part haunted house, part choose-your-own-adventure, and part jungle gym.

Most-visited and most-photographed slot canyon in the American Southwest.

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

On the Oregon coast there is a natural hole that seems to be draining the sea.

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

A collision of human error and natural geothermal pressure created this rainbow-colored geologic wonder.

A crumbling hospital from the 1850s on Roosevelt Island.

This iconic L.A. bookshop is housed in an abandoned bank—both symbolic and chic.

Rippling sand dunes frozen in the Arizona rock.

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

World's largest collection of serial killer artwork and other macabre exhibits.

A terrific purveyor of natural history objects and curios.

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

A bronze sculpture honors the 12 black students who attended the first integrated public high school in the segregated South.

The secret city built by the Manhattan Project.