A floating cat sanctuary on an Amsterdam canal.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

Scattered throughout London are ancient remnants of the city's former bounding wall.

The spiral staircase hidden inside this giant Parisian column was likely built for Catherine de Medici's astrologer.

The water-powered carriages are long gone, but for over a century this funicular railway has been the fastest route to the highest point in Paris.

This surreal statue brings a famous French novel about a supernatural cad to arresting life.

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

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

A lone cannonball remains lodged in the walls of the Hotel de Sens as a sober reminder of a revolution.

This former “ante-chamber to the guillotine” has been refurbished to illustrate the brutal history of French justice.

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

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

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

Statue of death tucked in the University of Medicine courtyard.

Paris' linguistic guide to the international language of, yes, love.

A scandalous Art Nouveau collaboration that set Paris all atwitter at the turn of the century.

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

The very center of Paris is surrounded by a bevy of strange good luck rituals.

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

Walk upon the mementos of the dead in this Parisian courtyard paved with medieval tombstones.

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

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

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

Notorious artist squat renovated into legal studios.