This massive underground salt mine now holds a sci-fi theme park in its depths.

An obscure public service from the U.S. government that redeems burnt, moldy, and soiled old greenbacks.

This Stockholm art museum integrates many of its pieces into the surrounding outdoor areas and natural landscape.

A Stockholm metro station is home to an escalator that is not only the longest in Sweden, but among the longest in the world.

Stockholm's narrowest alley is barely over two feet wide.

An ancient Viking runestone hidden in plain view in Stockholm's old town.

Sweden's "good old days" painstakingly re-created in a model village.

Stockholm's deepest subway station is also a stunning ecological wonder.

It houses the remains of a 17th-century version of the Titanic.

This little museum is making sure that the art and history of the graffiti sticker is not scraped from history.

From toys to kettles to scientific instruments, this German museum celebrates the beauty of 20th century design.

A collection of abandoned typographic signs from Berlin and beyond.

A fascinating insight into daily life in the Eastern Bloc.

Gardens representing parts of Asia, Europe, and the Mid East are tucked away among the Soviet-style buildings in East Berlin.

A wunderkammer of mysterious objects and stories.

A museum dedicated to the history of a terrifying secret police is now held in their former headquarters.

A 200-year-old collection of medical paraphernalia in a historic house.

Twisted trees shaped by coastal winds make this woodland look like something from a spooky story.

Believed to be the smallest castle in Europe.

This Japanese-inspired labyrinth of hot springs is hidden in a Chilean forest.

See hundreds of herons and egrets in the heart of the city in this dreamy hidden park.

A spectacular walk on the flank of a gorge.

Colorado's only active volcano last erupted around 4,000 years ago.

It takes a nine-mile hike to reach these hot springs, but weary hikers are rewarded with stunning views and a warm soak.