This colorful artistic feature atop a Danish art gallery allows visitors to stroll through a rainbow.

Walk 2,300 feet above the ground on the "Troll's Tongue."

In the hinterlands of Serbia's capital, a giant reflective mushroom houses an aeronautical history of the former Yugoslav republic.

Destroyed Serbian army headquarters sits half crumbled in a largely revitalized Belgrade.

A pair of connected skyscrapers form this symbolic gateway.

This one-time health resort was used by aristocrats around the world.

Soaring over 6,000 feet in the Bavarian Alps, this beer garden was once Hitler's 50th birthday present.

The world's greatest slide descends 18 stories from this looping mountaintop viewing platform.

This Nazi ruin was the site where Hitler was almost blown up by a suitcase bomb.

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

The deepest metro station in the world.

This attraction was abandoned after the Chernobyl disaster.

The ghost town left by the worst nuclear disaster of all time is being taken over by nature and urban explorers.

Thanks to its heroic service during WWII this Soviet castle has been turned into a monument towered over by a brutalist titan.

One of the largest museums in Ukraine remembers the story of the German-Soviet War in iconic, brutalist style.