An underground city of ancient quarry tunnels hid thousands of Allied soldiers in WWI.

Even France's favorite aquatic son Jacques Cousteau, couldn't get to the bottom of it.

An Orthodox church built by the Royal Family for the Russian community exiled to the French Riviera.

French commune at the heart of conspiracies.

The ruins of a medieval castle linked to the murderous French lord that inspired the famous legend of Bluebeard.

From carts to cars, this leftover Roman bridge in France has managed to survive for centuries.

For over 300 years this little carving has been the city’s good luck charm.

The opulent home that inspired Tintin's Marlinspike Hall and the adventures within.

These medieval ruins have survived since the 12th century, even providing shelter from the Nazis.

Legend has it this 11th-century castle was paid a visit from the devil.

Nicknamed the "Museum of Horrors," this French anatomical collection has been fascinating visitors for over a century.

The mummified heart of Louis XVII, the lost dauphin of the French Revolution.

Series of underground houses inhabited continuously for centuries.

This modern museum of Mediterranean culture is surrounded by a surreal concrete honeycomb.

An unsettling shrine dedicated to the ravenous beast that prowled 18th-century France.

There is a strange little carving of a person seemingly crushed by a pillar behind the remains of St. Thomas Aquinas.

Jean Tinguely's bizarre monster sculpture is hidden deep in a forest.

An architectural oddity of six stories, accessed by graceful ramps.

Green labyrinth formed by a karstic maze hidden in a preserved oak forest.

This otherworldly French waterfall looks like its waters have turned to stone.

The sunken structure looks like the victim of a catastrophic flood.

A sanctuary for wolves in a community which once trembled in fear of the murderous "Beast of Gévaudan."

This ancient theater was once the home of fierce gladiatorial battles.

Natural mummies hidden in the crypt of a medieval French church.