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

What looks like a normal building is really a hollow facade hiding a subway vent.

Indents in the pavement are all that remain from a grisly death machine in Paris.

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

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

A counter-culture bookstore like no other hides in plain sight in the streets of Paris.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

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

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

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

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

This impressive collection of rare books on ancient mysticism inspired author Dan Brown.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.

This 22-floor tower's Skydeck offers panoramic views of Amsterdam.

This gorgeous reading room houses the oldest and largest art history library in the Netherlands.

Barça football fans might see the insignia hidden in a church window as a divine sign.

The studio of Catalonia's most famous theatrical designer remains exactly as he left it.

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

The 2,000-year-old Roman columns are hidden within Barcelona's Gothic Quarter.

Week-long block party becomes a competition for the best decorated street.

Gaze upon chocolate sculptures depicting everything from chariot races to Gaudí's famous church at this shrine to sweets.

This semi-secret storybook hedge maze is also the oldest garden in the city.

Are they the remains of a fallen hotel, or the final stronghold for escaped Nazis?

A mysterious architectural gem in one of the most elegant areas of Buenos Aires.