An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

The deserted pirate-themed restaurant still entices explorers.

The personal library of the founder of modern neurology is open to visitors.

Two stone columns flank the grand Venice square, but there were supposed to be three.

Go inside to really appreciate this 500-year-old technological masterpiece.

This Venice bookstore has resigned itself to constant flooding by keeping its books in bathtubs and boats.

The remains of the left arm of the levitating philosopher-saint are kept in a 13th-century Neapolitan basilica.

This magical-looking island is notorious for the misfortunes suffered by its owners.

A labyrinth of ancient tunnels hidden below the city holds the ruins of 2,500 years of history.

A large grotto built in the 16th century amidst Florence's famous Boboli gardens.

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

One of several skulls claiming to belong to the beheaded St. John the Baptist is on display at this Roman church.

Jesus' footprints and the first catacombs in the world.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.

This massive library holds what was once the largest book collection in the world.

The encased skull that is widely believed to belong to St. John the Baptist.

A chapel on a volcanic core, marking the end of a successful journey.

This little-known relic crypt holds stolen parts of a Roman Empress.

A medieval military street hidden beneath a charming French fishing village.

The recovered bones of martyrs slaughtered during The Terror are on display in this church crypt.

An ancient monastery, a locked room, and a mysterious book heist.

A popular shrine where the Blessed Virgin allegedly appeared in 1830, displaying a holy armchair and two incorruptible remains of Lady Saints.

The famous winding walk at Chartres is surrounded in mystery and myth.