Every half hour, the flow of this unusual spring cycles between a rush of water and barely a trickle.

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

This roadside shrine to an unofficial saint has welcomed the wishes and prayers of local believers for generations.

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

Two awe-inspiring globes from the reign of the Sun King hang from the ceiling of France's national library.

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

The first green space constructed on an elevated viaduct.

A tribute shrine where the Space Invasion street art movement started.

Dishes are packed with flavor at one of the only Singaporean restaurants in Paris.

Known as the "Dodo Manège," this carousel features a herd of animals that have disappeared—or may be gone soon.

A haunting collection of the vanished and disappearing natural world.

Natural history museum celebrating biodiversity with a parade of taxidermy animals.

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

A surrealist timepiece by the artist of melting clocks.

This 400-year-old tree is actually an immigrant from North America.

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

The narrowest street in Paris.

The tradition of open-air secondhand and antiquarian bookselling in Paris dates back to the Renaissance.

If you look closely at the oldest bridge in Paris, you might notice hundreds of ugly faces leering from its sides.

An isolated 17th-century chapel on a remarkable site once dedicated to Celtic sun worship.

One of the last Breton ossuaries still preserving the bones of the dead.

A granite rock formation littered with various species of moss, lichen, and fern.

If they push on just the right spot, even the weakest person can move this titanic boulder.

A remote hilltop covered in giant monoliths haunts the Brittany countryside.