The remains of a town so thoroughly destroyed by French forces that the citizens simply left.

This picturesque Umbrian city has a subterranean side that has long remained hidden.

The astonishing collection of an infamous criminologist.

This real life asylum of horrors is now an abandoned ruin that hides the unbreakable code to one patient's insanity.

Medieval town turned hippie commune, once home to the secret foreskin of Jesus Christ.

An Italian ghost town that fought obscurity, until a mysterious illness brought it to its knees.

Long-abandoned art nouveau baths beneath Milan's Piazza Oberdan.

An underground paleo-Christian burial site composed of the remains of several cemeteries and Basilicas.

Brass cobblestones mark the places where individual Holocaust victims were taken from their homes.

This ancient Roman prison is decorated with an upside-down cross not as blasphemy but as saintly tribute.

Filled with goldfish swimming in a shallow pool of sea water, this ancient crypt is more wishing well than burial site.

One of seven Jewish catacombs in Rome and one of only two open to the public.

Abandoned medieval hill town.

This sword isn't waiting for a king to pull it out. It was placed there by a saint.

The location of the last witch trials of Italy, known as "The Salem of Europe."

This domed temple was built in a hidden cave mouth as a refuge for sinners seeking absolution.

Dug as a secret royal escape route, the tunnel became a wartime bomb shelter and dumping ground for vintage cars.

Inside this McDonald's you can dine on your Big Mac and fries next to a 2,500-year-old Roman wall.

One of the most important yet well-hidden museums dedicated to the history of medicine.

Surreal riveted sea forts once protected the Kent shores from German attack.

The last inhabitants of one of the U.K.'s most remote islands were evacuated in 1930.

Skulls and skeletons are omnipresent in this church dedicated to souls trapped in purgatory.

A cave in southern Italy adorned with thousand-year-old Biblical frescoes existed in obscurity until fairly recently.

Though an earthquake destroyed this village in 1980, one former resident still walks its streets every day.