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

This "floating railway" is one of the world's oldest monorail systems.

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

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

Where once there was a train station bathroom, there is now this German burger joint.

This Berlin island is home to a flock of free-roaming peacocks, as well as a historic ivory folly.

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

Ruins of a German Castle on top of a towering stone pillar.

This medieval castle overlooking the Elzbach river looks just like it did hundreds of years ago.

A narrow passage next to a cafe leads to a courtyard exploding with murals, tags, and paste-ups.

The largest free-standing aquarium in the world resides in a hotel lobby in Berlin.

A surreal museum of extraordinary industrial objects.

The most visited, and possibly most controversial, museum in Germany.

A whimsical and twisted animatronic monster tour beneath the streets of Berlin.

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

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

Catacombs turned marketplace.

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

One part local history, 99 parts gruesome haunted house.

A charming 17th-century alley is lined with secondhand bookstores and antiquarian shops.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

Nine centuries-old fortresses guard the walls of this medieval Romanian city.

Over 100 towers were built in Bologna during the Middle Ages, but only 22 survive.

Enter the cabin of a life-sized Hindenburg replica.