This French "sea of rocks" is packed with stunning rock formations and its own medieval castle.

100-windowed castle turned art gallery, built by one dedicated mason.

Series of underground houses inhabited continuously for centuries.

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

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

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

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

The deserted pirate-themed restaurant still entices explorers.

Statue of a decomposing prince that once held his heart in its hand.

An art world insider finds himself battling for his artistic home.

This French castle is said to have once held the Holy Grail but is now a gorgeous mountaintop ruin.

A well-preserved medieval village nested on a rocky outcrop and surrounded by a network of cliffs, natural bridges and canyons.

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

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

This salt marsh in Southern France is as pink as the flamingos that inhabit it.

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

Historic medieval fortified city in southwest France.

A beautiful and classically designed villa, with an hourly infestation of monsters.

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

Known as the "Dodo Manège," this carousel features a herd of animals that have disappeared—or may be gone soon.

This museum houses an imposing skeleton army comprised of creatures great and small.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

Notorious artist squat renovated into legal studios.

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.