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

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

Lyon, France is home to two remarkably preserved Roman theaters, one dating back to 15 BCE.

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

A mosaic-tiled house built by graveyard sweeper Raymond Isidore.

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

This is what trains will look like after the zombie apocalypse.

These quaint French houses dangle precariously over a precipice.

For hundreds of years, automatons moving to metallic music have been marking the passage of time.

A Gothic cathedral created from volcanic rocks.

This historic island prison holds one of the dungeons from the Count of Monte Cristo even though it is a work of fiction.

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

See the nearly two-century-old ruins of pre-railroad America at the former site of a lock on the Ohio and Erie Canal.

An abandoned, rusty old relic of railroad history stands at attention over the Cuyahoga River.

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

Historic medieval fortified city in southwest France.

The ruins of a Duke's bucolic dream, where camels once roamed alongside "Dutch" windmills and faux-Italian vineyards.

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

The first green space constructed on an elevated viaduct.

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

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

This museum houses an imposing skeleton army comprised of creatures great and small.

France's national museum of scientific and industrial instruments.

One of the oldest medical collections in Europe focusing on rare surgical instruments.