This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

Notorious artist squat renovated into legal studios.

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

The macabre collection of Jacques Sirgent, an expert scholar on the undead and all of their trappings.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

This quaint Italian town keeps losing ground as the sides of its plateau slowly erode.

This building has a giant piercing through one of its corners.

A landmark in the history of technology and computing is hidden in a tiny Baroque chapel.

When this funny little building went up in the 19th century, most people thought it would simply fall over.

The astonishing collection of an infamous criminologist.

A fake medieval village in the middle of Turin.

Now an entertainment complex, the Lingotto building was once an avant-garde auto factory with a test track on the roof.

An otherwise quiet campground becomes a bustling medieval town for two weeks every year.

This ancient hydrological marvel is now the base of a modern outdoor cinema.

The railway carts travelers to central Athens's highest peak, which offers stunning vistas of the city.

Ancient ruins hidden underneath a modern luxury hotel.

The skull of the patron saint of lovers lies in the Basilica di Santa Maria in Cosmedin—maybe.

The yawning maw of this pagan visage is said to bite off the hands of liars.

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

More sculpture than building, this architecturally significant temple was built on the spot of Saint Peter's crucifixion.

The mystic whose incorrupt corpse still attracts the faithful.

This subterranean shrine beneath a bike rental store celebrates the iconic Italian scooter.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

St. Francesca Romana, patron saint of drivers, resides in the church she founded.