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

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

A daring D-Day assault by U.S. Army Rangers is commemorated atop the high cliffs of this strategic point.

The castle was reconstructed to fit Kaiser Wilhelm II's romanticized vision of the Middle Ages.

A centuries-old complex of hand-dug stone chambers has sheltered locals in times of trouble.

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

A swath of France so devastated by war it is still forbidden to go there.

The post-apocalyptic remnants of a bucolic town ruined by a plane crash.

The deserted pirate-themed restaurant still entices explorers.

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

A place to see how French aristocrats lived in the early 1900s.

A huge Megalithic chamber tomb located behind a cafe.

Legend has it this 11th-century castle was paid a visit from the devil.

An underground city of ancient quarry tunnels hid thousands of Allied soldiers in WWI.

This striking fort on the Maginot Line looks just as it did after being destroyed in the Fall of France.

This castle-fortress is a living example of the transition from medieval defenses to modern fortifications.

Now a memorial, this factory was once used as a concentration camp for artists by the Vichy government.

A suspended footbridge allows for traversing this gorge carved through the French Alps.

A castle-like sea fort from the 17th century is now a museum to oyster farming.

The eclectic observatory castle of a 19th-century astronomer and explorer.

Longest canal tunnel in the world, abandoned in the 1960s.

Fighting the British and making game shows for over 150 years.

This former limestone quarry is now a subterranean wonderland of grand stonework.

A medieval church built into an ancient cave.