Revitalization efforts converted a former U.S. military heliport into a sprawling urban park.

This unique structure allowed boats to bypass underwater mine barriers in the channel to enter the harbor.

Large, airy hallways hide within an impenetrable fortress that beckons urban explorers.

This picturesque medieval monastery guards a small trove of historic treasures.

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

An imperial church bombed to ruins during WWII now stands as a jagged memorial.

A restaurant and observation deck built in a unique broadcasting antenna.

A traditional U-Bahn station in Berlin gets a string of rather untraditional benches.

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