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

The history of radiation is on safe display at the foot of a radiation science laboratory.

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

Down a cobblestone alleyway is a museum dedicated to Romanticism, with a secret garden.

A subterranean shelter remains intact under a busy Paris railway station.

A museum on the history of Paris, including a set of Napoleon's toiletries, Proust's room, and relics of the Revolution.

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

19th century pendulum and a clock restored by a rogue group of guerilla artists.

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

Egyptian Revival movie palace abandoned for decades and restored in 2013.

A Parisian cemetery where the elite and artistic are interred beneath an eccentric collection of tombs.

This statue was given to France by the United States to commemorate the centennial of the French Revolution.

France's national museum of scientific and industrial instruments.

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

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

A museum of carnival attractions where you are invited to ride the rides.

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

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

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

The oldest stone house in Paris was built by its most famous alchemist.

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

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.