Bizarre Cavern.

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

The former locus of Boston's high culture has been shuttered and buried for over 70 years.

Beneath the mossy overgrowth covering this once-sprawling campus lies decades of history and the secrets that come with it.

The remains of a failed attempt at medieval nerdery are hidden deep in the woods of Virginia.

North America's oldest quarantine facility was built in response to Philadelphia's 1793 yellow fever outbreak.

This Tennessee manse was built so opulent that the very utilities doomed it to fail.

Decades after testing the polio vaccine on unwitting patients, this historic mental hospital sits in ruin.

This lovely university observatory continues to sit abandoned since its potential savior was sent to jail for fraud.

The abandoned husk of a mental institution that failed to save a Jazz Age icon still sits nearly unchanged.

This abandoned Poconos resort is haunted by a history of kitschy romance and a violent fugitive.

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

These World War I shooting range tunnels are now haunted halls of underground graffiti accessed through the roots of a tree.

An abandoned 1920s school with a mysterious history.

This abandoned psychiatric hospital once housed more than 4,000 patients in the middle of a quaint New England town.

This abandoned school has had many lives since the early 1900s, and all of them doomed.

An iconic steel and chrome diner from the 1940s left empty for nearly 20 years is in danger of being demolished.

An eight-sided home built during a brief octagon craze in the 1850s.

A historic recreation of the golden age of the Erie Canal, abandoned for some time, slowly being restored.

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

Locals dubbed this abandoned abode the "gingerbread house" because of its odd architecture.

Ruins of a historic medical facility sits eerily by the water.

The NBA player's elaborate former home is now a ghost of its old glory.

Enchanting gardens surround a derelict mansion, all hidden in plain sight behind a stone wall.