Tens of thousands of ancient rock carvings hidden in the heart of a French national park.

French commune at the heart of conspiracies.

These medieval ruins have survived since the 12th century, even providing shelter from the Nazis.

The opulent home that inspired Tintin's Marlinspike Hall and the adventures within.

A massive, secret marina for the Nazis' most formidable weapon in the Atlantic.

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

Underneath a chalk hill in France lies what Hitler hoped would be the underground launching base for a devastating new weapon.

The birthplace of the ferocious William the Conqueror, this castle is awash in medieval history.

This narrow path was cut right into a French mountainside to feed the country's early naval expansion.

Despite centuries of architectural innovation, this French castle is being built like it's the 13th century.

One of the world's most complex timepieces.

The Church of the Annunciation was carved into the face of a cliff, just like the rest of the town of Haute-Isle.

If they push on just the right spot, even the weakest person can move this titanic boulder.

A quaint medieval millhouse hovers surprisingly above the waters of the Seine.

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

This collection of French root art looks like an indoor fairy wonderland.

This medieval tower is all that remains of the castle where Joan of Arc was held before being burned at the stake.

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

A chapel on a volcanic core, marking the end of a successful journey.

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

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

A public park off the beaten path with a beautiful waterfall and 13th century Cistercian abbey.

This stunning French estate was so lavish that it landed its original owner in jail for the rest of his life.

This ancient Roman bridge and aqueduct still stands as a wonder of classical construction.