Boats must transform into railroad cars to navigate this Polish canal.

This imposing 20th-century castle was abandoned before it was ever completed.

An abandoned Nazi explosives plant founded by the inventor of dynamite is now an underground museum.

An underground city of salt.

At this Arctic outpost, get to know members of the indigenous Sámi community and meet their herds.

Home to three historic ships from the age of Vikings.

This 18th-century project to build the world's tallest gravity dam was never completed.

A pair of gigantic baby heads greet passengers at Atocha Station.

Inside this church are the alleged remains of the patron saint of lovers, epileptics, and beekeepers.

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

This small and often-overlooked museum holds some of Spain's finest artistic treasures.

The only urban monument in the world designed by the great surrealist painter Salvador Dalí.

The morbid items in this small and hidden museum are not for the weak stomached.

This amazing abuela became a diehard metal fan late in life and an icon of Madrid's '80s rock scene.

Over two centuries old and counting, Madrid's massive botanical garden contains one of Europe's only desert environments.

This museum documents the ancient practice of salt production in Figueira da Foz.

This impressive rupestrian engraving dates back to the Upper Palaeolithic period.

An 11th-century medieval castle cascades over the town of Numão.

Tucked away inside this concrete building is a church and its grand display of brutalist architecture.

One man's remarkable private collection of art from around the world.

Local lore says the devil built this beautiful medieval bridge to help a fleeing bandit.

This abandoned five-star hotel is now a five-star urban exploration destination.

A stunning 18th-century site where pilgrims ascend by a series of punishing stairs only to return via funicular.

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