The largest underground church in Europe.

The world's largest solar furnace uses 10,000 mirrors to concentrate the sun's rays to generate power.

Small French town or alien garage?

French commune at the heart of conspiracies.

A 14th century bridge built as a fortress, where the devil lurks on one of its towers.

Ancient paintings known as the "Sistine Chapel of Cave Art."

A French library that makes sure its love of books is writ large... giant in fact.

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

The mental institution where Van Gogh created some of his most famous work now allows guests to walk in the artist's footsteps.

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

Perhaps the most beautiful of preserved saints, with a little help from Paris.

A house of bones — but nobody is quite sure to whom they belong.

One of the world's most complex timepieces.

A colossal sculptural lion built by the same man who designed the Statue of Liberty.

An overlooked marble is the only surviving in-place 18th century example of the measurement that changed how we define distance.

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

There has been an astronomical clock on this spot since the 14th century.