The world's largest underground iron ore mine.

The world's first ice hotel is still one of the most elaborate and beautiful.

The three colorful women depict characters from a beloved children's story.

Sweden's first nuclear reactor, R1, can be visited 25 meters underground.

An iconic and controversial ancient Iberian funerary urn with a hauntingly penetrating gaze.

Its appearance in "Game of Thrones" may spur on the long-awaited restoration of this medieval shipyard.

This former charity hospital for elderly clergy houses some of Seville’s most treasured paintings.

The final resting place of the great navigator, or maybe his brother.

Fascinating exhibits of prehistoric and ancient artifacts displayed with a uniquely modern touch.

A well-restored ancient archaeology site gives a real feel for life during the Roman age.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

The astonishing collection of an infamous criminologist.

One of the tallest buildings in Iceland, and perhaps, the most visually impressive.

One of America’s oldest and spookiest hotels, thanks to the residency of ghosts, dead presidents, and Alfred Hitchcock.

Hundreds of hidden passageways weave through the old quarters of Lyon.

This old Estonian mine has been kept like a sprawling time capsule of the local shale industry.

Disused seaplane hangar gets a second life as the jaw-dropping home of Estonia's museum of maritime history.

Man-made mineral caves house massive bat colony.

A former imperial sea-fortress and Soviet prison.

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

This scale model of our solar system hid in plain sight for years before a physics team sought out all the planets.

Head underground and take a tour of the city's working sewer system, and see the underground river Senne, which defined Brussels for centuries before being covered in the 19th century.

Theme park featuring miniature replicas of European monuments.

Vienna's underworld of tunnels and subterranean rivers made an iconic appearance in a 1949 Orson Welles film.