German and American troops joined forces to defend this fortress during the strangest battle of World War II.

An officers prison camp believed to be impregnable by the Germans saw over 30 successful escapes.

Holding the most bodies of any cemetery in the United States.

A unique attraction and museum dedicated to exploring iconic roadside structures.

100-windowed castle turned art gallery, built by one dedicated mason.

Relive a Polish uprising via an enormous, century-old cyclorama.

A galaxy of glowworms—larvae of a gnat—hides deep in the belly of these caves.

A labyrinth of ancient tunnels hidden below the city holds the ruins of 2,500 years of history.

A cave 150 feet beneath Kansas City is the perfect climate for growing 10,000 delicate orchids.

A cavernous three-story, 43,800-square-foot basement that was forgotten about for 60 years.

Accessible only at low tide, the deserted island is dotted with World War II ruins.

The heads of two giant mythological water horses honor Scotland's horselord past.

One of the oldest scientific gardens in Britain, containing more than 13,302 plant species in its core collection.

A hidden tunnel leads to a medieval queen's shrine buried beneath a parking lot.

One of Europe's oldest libraries.

Nondescript elevator doors open to reveal a stunning, surreal world.

This 11th-century temple gave rise to the word "juggernaut," as well as some mysteries that defy scientific explanation.

Tour the world's largest deep-hole dimension granite quarry, where you can view the plant where gravestones are made and roll a ball down the outdoor granite bowling alley.

The romantic botanic tunnel feels like a well-kept secret.

Oregon's unexpected high desert, displaying layers of time in a colorful show.

This frequently-photographed waterfall takes only a short hike to visit.

This lake in the Cascades lives up to its name, disappearing down a hole every spring.

This extinct shield volcano is the lightning rod of the Cascades.

Hollowed out cedar log tubs set in an ancient towering forest.