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

A remote hilltop covered in giant monoliths haunts the Brittany countryside.

The world's most famous cheese caves.

A massive, secret marina for the Nazis' most formidable weapon in the Atlantic.

This narrow path was cut right into a French mountainside to feed the country's early naval expansion.

Underneath a chalk hill in France lies what Hitler hoped would be the underground launching base for a devastating new weapon.

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

These crumbling Nazi artillery bunkers are now fair game for massive graffiti projects.

A bike train runs along a disused railway line through the tranquil French countryside.

The post-apocalyptic remnants of a bucolic town ruined by a plane crash.

The Argonaute submarine was the French navy's pride and joy in the 1950's.

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

A swath of France so devastated by war it is still forbidden to go there.

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

Sleep in a climate-controlled plastic bubble for the night.

Architect Le Corbusier built his friend a cubist house to match his impressive collection of cubist art.

This is what trains will look like after the zombie apocalypse.

A natural arch carved by a river gave its name to the so-called "Cave of Forgotten Dreams."

An iconic and eccentric bar for "Manouche" Jazz music keeps expanding its space—and its influence.

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

These quaint French houses dangle precariously over a precipice.

This modern French ossuary contains the jumbled bones of 130,000 WWI soldiers.

Massive puppet-automaton machines created by French artist collective Machines de l’Ile.

This stunning natural double arch, the largest in the Alps, went undiscovered until 2005.