Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

This cemetery features modernist statues as strange as its name.

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

One of Catholicism's four major basilicas has a series of papal portraits that are said to predict the end of the world.

A treasure trove of Renaissance-era funerary art in a Roman church built on top of Nero's grave.

An eccentric artist's abode in this small Italian town has been transformed into a surreal temple of mosaic madness.

Naturally preserved bodies are eerily staged throughout the crypt in varying poses.

Charles Dickens was not a fan of the ghastly wall dressings in this 6th century church.

Italian poet Dante Alighieri is entombed in this small mausoleum in Ravenna, and his hometown of Florence has never been too happy about it.

A domed disco abandoned since the '70s now attracts artists and explorers under its unique roof.

An incredible menagerie of more than 3 million taxidermied animals at the oldest science museum in Europe.

Europe’s oldest natural human mummy.

A stunning cemetery famous for its extraordinarily delicate & lifelike mourning sculptures.

A dismembered holy head stares out from her beautiful reliquary at the St. Dominic Basilica.

One of the world’s smallest bars, just 13 square feet, is brimming with speakeasy flair.

One of the largest caves in the world open to the public.

A sunken idol welcomes parishioners to Davy Jones' Locker.

Where Aleister Crowley taught magick in "La Chambre Des Cauchemars," his "Chamber of Nightmares."

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

This enchanting 600-year-old tree is so magical it inspired the beloved tale of Pinocchio.

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

David Sedaris called it "The greatest shop in the world."

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

Skulls from the plague of 1656 and World War II bombings are united by a cult dedicated to caring for the ancient dead.