This abandoned coliseum was intended to be a grand Nazi rallying ground before it was halted at the end of the war.

Money made from smuggling sugar helped create this wondrous rock maze in honor of the Prussian Queen Louise.

A spiral staircase twists to the top of this unusual Czech lookout tower.

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

Buried five stories underground, this Soviet bunker is packed with gas masks and Cold War paraphernalia.

Europe's largest natural bridge has a 19th century royal chateau built into its side.

This Prague museum collects brutalist relics and memories from the country's former Soviet rule.

Europe's second largest ossuary wasn't discovered until 2001.

A collection of anatomical samples from one of the first anthropologists to suggest that humans reached North America by crossing the Bering Strait.

A church of bones, decorated with 40,000 human skeletons.

This spire on an Austrian mountain is wrapped around a long spiral slide and has the world's tallest wooden observation deck.

This skeleton-filled altar piece served as a backdrop to one of the most iconic scenes in "The Sound of Music."

There are two dozen tanks just sitting in an open field in Lower Saxony.

The abandoned mine where American troops discovered a treasure trove of art and artifacts hidden by the Nazis.

A strange rock formation with numerous legends trying to explain it.

The world's tallest church tower reveals a spectacular view to anyone up to the task of climbing the daunting staircase.

A former ironworks that was the first UNESCO industrial site.

Ample proof that watery ends make for well-preserved, millenia-old mummies.

Dress up like a miner and take a slide into the disco-lit depths of this once foundational salt mine.

A Black Forest cuckoo clock theme park features one timepiece big enough to walk inside.

The industrial monstrosity known as Bagger 258 is a colossal mining machine built in the DDR - but now left for dead in a German field.

This German bone house contains the remains of some 20,000 souls.

No need to strap in for a "ride" on this walkable roller coaster.

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