This abandoned lighthouse looks like a rusting oil rig, but has managed to survive a number of storms.

An acoustic anomaly with a mysterious cause.

Hidden behind Lincoln's head is a 70-foot-long chamber containing enamel plates documenting American history, sealed in a teakwood box in a titanium vault.

Hidden in a secluded Greek cove is a pristine beach marred only by the rusting smuggler's hulk stranded on its shores.

This maze-like slot canyon is a unique gem within an already fascinating geological area.

This little-known Revolutionary War fort is supposedly haunted by the ghosts of its past.

Once the world's largest reinforced concrete structure, this abandoned bridge now beckons urban explorers.

Buildings that dynamite couldn't bring down were abandoned because of bathroom issues.

This huge, disused viaduct is now a crumbling concrete underworld of covered in years of graffiti.

A toxic ghost town sitting atop a massive coal fire.

A mysterious monument meant to be a guide into "an Age of Reason" was destroyed after an apparent bombing.

A scenic fort on the harbor protected Philadelphia from an attack that never came.

This Great Depression-era creation was once known as the strangest house in the world.

The remains of an old sawmill, gristmill and the surrounding industry dating back to the 18th century.

World War II bunker still standing on the New Jersey beach.

Hidden in plain sight on the Hudson River is an abandoned train station where nature has taken over.

Where America's first doomsday cult awaited the end of the world.

This tiny New Jersey village has lived many lives but seems determined to remain a ghost town.

In the woods of New Jersey lie the ruins of a munitions village abandoned after World War I and the remnants of a 1920s wooden racetrack.

How this Pine Barrens hill got its name is uncertain, but on a good day the view from the fire tower is crystal clear.

Rising out of a clearing in New Jersey's Pine Barrens is an Aztec-inspired monument to the "Lindbergh of Mexico."

A historic grist mill and active sluice on the Black River.

A recently abandoned psych ward at the end of Sanatorium Road.

Mysterious rocks that ring musically when struck.