The former Nazi concentration camp stands as a museum to remember this dark chapter in European history.

Poland's oldest salt mine has nearly everything one needs to live underground forever.

An underground city of salt.

An underground city beneath Krakow's postwar socialist utopia.

Where visitors can play more than 150 retro arcade games.

At first glance, this area seems like just another city park, but the lush landscape hides a dark past.

The unsettling remnants of a torn down movie set lies nearby the ruined location of the actual Płaszów Labor Camp.

This Polish cave has housed a dragon, a brothel, and an enduring legend.

A collection of modern and vintage pinball machines housed in the cellar of a 15th-century building.

Beneath Kraków Old Town's main square lies a hologram-filled medieval market vampire graveyard wonderland.

St. Mary's features one of the most spectacularly decorated cathedral interiors in all of Europe.

The collection of signage remembers the midcentury pushback against the new neon light.

From mining complex to industrial exhibition, this museum once played a major part in the X-Files.

A spoke-tacular artwork constructed from recycled bicycle rims.

Home to a full cast of the largest woolly mammoth ever recovered in North America. 

A hulking remnant of Alaska's industrial gold mining boom in the 1920s.

North America's first frozen mummified remains of an ice age steppe bison, the 36,000 year-old mummy named "Blue Babe."

One woman's dream became a train hotel in her backyard.

This frozen tunnel in central Alaska is both an engineering feat and a valuable climate classroom.

This small town in the Netherlands has no roads but instead, miles of canals and over 100 bridges.

This artificial ring island was built to hold cubic tons of polluted dirt.

A modern reimagining of a medieval city gate.

These slanted cubic abodes are a creative if odd solution to a zoning pickle.

Birthplace of the "Cat in the Cradle" and a cluster of iconic, original windmills that let the Dutch tame the seas.