A 12th-century fortress containing some of Berlin's oldest buildings.

Beneath the impressive baroque cathedral that rises from the center of Berlin lies the largest collection of Prussian royals in the world.

Named after a militant urban guerilla, this famous former squat is a graffiti-covered stronghold of leftist culture.

Berlin's oldest surviving academic architecture hosted decades of animal dissections.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

The music is over at the Ballhaus Riviera Ballroom, but the ballroom remains in haunting disrepair.

Berlin's natural history museum houses the world's largest mounted dinosaur and the late beloved polar bear Knut.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

On the Spree bank, discover one of the last reminders of a symbolic wall that divided, and was torn down by the people.

A tree-like building perches on its trunk in the Steglitz neighborhood of Berlin.

Started as a kitchen garden, now the second largest botanical garden in the world.

This futuristic German spa allows visitors to float in a pool of salt water while zoning out to underwater techno.

A slice of central Asia in the middle of Berlin.

A once-secret library of Freemason history in Catalonia.

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

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

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

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

A Hawaiian stairway to heaven—that you can't climb.

A beautiful geyser under environmental threat.

An underwater city for the dead.

This fantastical waterfall is hidden in a cave located in a cracked cliff.

Pompeii's less famous neighbor is still revealing her secrets.

Centuries-old bridges grown from tangled roots.