The only swimming pool listed on the National Register of Historic Places is emptied and refilled each day with naturally filtered water.

Stalactites and stalagmites in a beautifully lit cave.

Virgil's many-mouthed gateway to the underworld.

A sulfuric hellscape in southern Italy.

More than five miles of underground passageways.

This historic Melbourne bullet factory is fully encased in a massive glass and steel cone.

Oxford University's stateliest library seems designed to make students truly feel the weight of knowledge.

Despite violent work crews and massive delays this abandoned canal tunnel was built to last into the modern day.

Bursting forth from a historic German neighborhood, these day-glo palaces are now a bright fixture in the town.

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

A pub that is literally in the middle of nowhere, but continues to do business.

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

This Oregon farm is dedicated to teaching people the professional art of tree climbing.

An illuminated manuscript comprising the life's work of a lone monk, inexplicably decorated with a portrait of Satan himself.

An old vending machine serves up unpredictable beverages from its seemingly magical insides.

This Seattle curio shop collects and sells haunted items in order to spread wonder one grim artifact at a time.

An alleyway plaque is all that remains of the independent Texas' envoy that forgot to pay their rent for over a century.

The signs of a long buried road can still be found hidden beneath a London sewer grate.

This charmingly homemade amusement park has been growing for 40 years.

This collection of illusory paraphernalia has been culled from the history of London's premier magician's club.

One of the few remaining casualties of the London Blitz, this destroyed church has become an enchanting public garden.

Spanking machines, fake goats, and more devices of humiliation are on display in this museum of fraternal initiation devices.

By day this New Orleans square is for pedestrians, but by night it is a kingdom of kittens.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.