Once a 19th-century brasserie, this McDonald's exterior celebrates Alsatian design and the "King of Beer."

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

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

An off-the-beaten-path boutique stuffed with an eclectic collection of upcycled goods.

The first green space constructed on an elevated viaduct.

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

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

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

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

This Parisian café sticks almost exclusively to an ethos of reuse.

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

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

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

Abandoned railway line circling the city of Paris.

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

France's most famous cemetery, with some of its most curious tombs.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

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

These ruins reveal the remarkably intact layout of a Roman marketplace.

This monumental mural crafted nearly 40 years ago is still in perfect condition.

This triumphal arch celebrating the Sun King's conquest of Lille is a masterpiece of military architecture.

Tables of secondhand books fill the inner courtyard of this 17th-century stock exchange.

Museum in a swimming pool where the water still flows.

This former cannon foundry and castle for the Counts of Flanders is now a public garden.