A miniature train-ride through Slovenia's largest cave system.

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

Two very green residential towers cleaning the air in one of Europe's most polluted cities.

An old slave lookout in Cuba's historic sugar cane fields.

Once a favorite playground for the world's most illustrious guests, Hotel Nacional's secret weapons and bunkers reveal a more menacing side to its golden history.

This island hill is strewn with boulders carved by shipwreck victims from the age of sail.

The largest Chinese cemetery in the world outside of China dates back to the 15th century.

Holy Hindu shrine in an enormous, monkey-filled limestone cavern.

This Slovakian statue of an emerging sewer worker might just be a bronze peeping tom.

Baroque celebration of the end of the Great Plague of Vienna.

The water-powered carriages are long gone, but for over a century this funicular railway has been the fastest route to the highest point in Paris.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

In Portugal, a secluded stretch of untouched natural beauty hides at the bottom of a steep hill.

Elaborate tile work in this railway station tells the story of Portugal.

Amsterdam's former hotspot for public executions and dissections.

The world's second largest single-dish radio telescope, once used to contact E.T.

Fantastic views and thousands of love locks.

The castle where Martin Luther secretly translated the New Testament from Greek to German while in hiding.

Tiny castle in the middle of the Rhine made you pay to pass.

Legendary site where an evil bishop was devoured by rodents.

The birthplace of Karl Marx is now a museum dedicated to the communist revolutionary's life and work.

This former Nazi castle was built as a school to train what would have been the future of the Third Reich.

Twisted buildings adorn the banks of the Rhine river.

Thousands of tourists and residents in Cologne affix "love padlocks" on the Hohenzollernbrücke Bridge to symbolize their affections.