Once the path of a railway tunnel, now home to thousands of glowing insects.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

Jesus' footprints and the first catacombs in the world.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

A labyrinth of ancient tunnels hidden below the city holds the ruins of 2,500 years of history.

Five candy-colored villages on the Italian Riviera.

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

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

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.

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

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.

The video game-themed street art first popped up in the French city.

Visitors dating back to the 1600s carved their marks in the stones of the iconic tower.

One of the most photographed buildings in a city known for its Modernista architecture is an abandoned squat.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

A surrealist timepiece by the artist of melting clocks.

The narrowest street in Paris.

Giant lamp houses the tourism information center.

Entering this curiosity shop is like stepping into a mad scientist's lab.

10,000 flowered plants bloom in the City of Roses.

The magic's in the hole!