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

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.

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

Nine centuries-old fortresses guard the walls of this medieval Romanian city.

The romantic botanic tunnel feels like a well-kept secret.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

Three bridges and one giant canyon make up this fantastic Spanish settlement.

The world's longest known cave system.

A student driver's nightmare.

Perfectly preserved ancient monastery in an impossibly dramatic location on a rocky island in the Atlantic.

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

A small, but award-winning beach known for its literally spotless reputation.

This weird abode has inspired everything from the "House On Haunted Hil" to a robot hunter's pad.

The longest hedge maze in the world.

Thousands of exquisitely carved stone water storage wells, hundreds of stone steps fill this exquisite medieval stepwell.

Monasteries on rock pillars, once accessible only by frayed ropes.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

The only swimming pool listed on the National Register of Historic Places is emptied and refilled each day with naturally filtered water.

A massive underwater sinkhole made famous by Jacques Cousteau.

Stepping away from the glitz of mobsters and casinos to learn about the other history of Vegas.

The first declared National Monument in the United States.

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

This futuristic German spa allows visitors to float in a pool of salt water while zoning out to underwater techno.

A hand-built folk art installation covered with messages of God's love.