A cave dwelling that was started by the Celts, expanded by monks, and finished by knights.

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."

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

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

This French ghost town from World War II has been left as a memorial to German atrocities during World War II.

A museum on the history of Paris, including a set of Napoleon's toiletries, Proust's room, and relics of the Revolution.

Medieval museum built over Roman baths that features famous tapestries of a lady and a unicorn.

This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.