An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

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

An underground city of salt.

The site of the first battle of World War II.

Real bones which are said to have belonged to a Polish dragon.

A tribute to the Polish insurgents who fought in the failed attempt to end their city's Nazi occupation.

A floundering Polish shipyard was once the soul of the Solidarity movement that capsized communism.

The Polish capital has had a deep connection to its guardian mermaid for almost a millennium now.

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

A hidden three-foot-wide house separates these two regal churches.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

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

This chimerical bridge/tunnel appears to dead end right into the sea.

Largest island in the Baltic Sea experiences such idyllic weather that roses bloom in the middle of December.

Swedish skyscraper with a 90° twist.

This trio of stone spires claims to be the only preserved medieval execution site in Europe.

A Gothic-inspired fish market is Gothenburg's best place to find loaves and fishes.

Legend has it that this large rock maze in Sweden was created as punishment by the daughter of a wealthy captain.

A nearly 500-year-old sculpture depicts a man eating a sack of babies, and no one is sure why.

The bears of Bern have been a city highlight for over 500 years.

One part local history, 99 parts gruesome haunted house.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

London's last remaining public soapbox site has seen speeches from Karl Marx, Vladmir Lenin, and George Orwell.

A community of artists and entrepreneurs seeks a simpler life on London's waterways.