This massive subterranean fissure is known as the "underground Grand Canyon."

This expansive bridge in the Canadian wilderness was originally just built for friends.

Dolphins, ancient clams and hundreds of waterfalls make this one of the world's top tourist destinations.

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

A Parisian cemetery where the elite and artistic are interred beneath an eccentric collection of tombs.

The world's most active stratovolcano is almost always erupting.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

The seamy, underground secrets of Portland's criminal past.

The largest underground church in Europe.

The feral felines of Roosevelt Island have a small army of allies and an abandoned hospital all to themselves.

Despite attempts by local police to discourage it, Beatles-inspired graffiti has been a means for artists to air grievances for decades.

This hospital once pioneered the use of electroencephalograms, but fell into maltreatment, abuse, and eventual abandonment.

Venice's "Island of the Mad."

Medicinal spa created with the discharge from a geothermal energy plant.

Resting place of Hollywood's immortals is also site of summer film screenings.

The decaying ruins of Wales' first asylum for the mentally ill.

A tiny museum housed in a New York freight elevator specializes in the "overlooked, dismissed, or ignored."

Two gravestones clasp hands over the religious divide.

An ice cream parlor chain that caters to vegans and pinball fans equally.

A island reachable by a causeway at low tide is possibly one of the earliest Western European locations to be identified in text.

Peek through the gates at this oasis from the city, full of Old English charm.

The one-time stronghold of the noble Douglas family, now home to ghost sightings and nesting birds.

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

One of the few remaining ancient aqueducts described by Frontinus as 'the most solemn testimony of the Empire.'