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

A Gothic cathedral created from volcanic rocks.

The largest underground church in Europe.

Historic medieval fortified city in southwest France.

This natural French spring has been turned into a magical grotto by Roman and medieval constructions.

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

An icy lake tucked among jaw-dropping alpine panoramas.

At Monet's beloved home you can still see the Japanese bridge, waterlilies, and weeping willows that were the subjects of some of his most iconic paintings.

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

Noirish green neon marks the location of one of the oldest private detective agencies in France.

Hundreds of hidden passageways weave through the old quarters of Lyon.

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

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

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

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

Behind the pink curtain, Au Bonheur du Jour, an art gallery of erotic archives.

"In the Dark" Restaurant in Paris offers dinner in complete darkness.

A favorite Paris bar for U.S. expats, including Gershwin, Hemingway, and James Bond.

Notorious artist squat renovated into legal studios.

This massive library holds what was once the largest book collection in the world.

Abandoned railway line circling the city of Paris.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

A counter-culture bookstore like no other hides in plain sight in the streets of Paris.

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