An isolated 17th-century chapel on a remarkable site once dedicated to Celtic sun worship.

An immersive projection art installation uses sound, scale, and light to take visitors inside classic works of art.

The 16th-century church was kept in its ruined state as a reminder of the casualties of World War I.

The personal library of the founder of modern neurology is open to visitors.

A self-built mosaic house and sculpture park.

One woman's decades-long obsession with the "La Fée Verte."

Museum in a swimming pool where the water still flows.

A French valley with forests so lush it was nicknamed "the Small Amazonia of the Pyrenees."

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

The great Italian Renaissance painter was laid to rest here in the Chapel of Saint-Hubert.

Beautiful carved tunnels.

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

BDSM, 1930s Style.

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

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

The only remaining collection of flayed figures made by French "madman" Honoré Fragonard.

This off-limits room in the National Library of France is home to a system of pneumatic tubes, once used to bring books to readers.

This massive blockhead sculpture hides an entire library.

Pitié-Salpêtrière was the dumping grounds for women who received the dreaded diagnosis of "hysterical."

Natural history museum celebrating biodiversity with a parade of taxidermy animals.

A modern-day Lascaux cave underneath Paris.

Twelve grave-faced marble angels guard the emperor's tomb at Les Invalides.

This former “ante-chamber to the guillotine” has been refurbished to illustrate the brutal history of French justice.

Sacked by Vikings, blessed by William the Conqueror, dealt a fatal blow during the French Revolution—these ruins have seen it all.