Catacombs turned marketplace.

A diminutive statue that was inspired by the sculptor's own daughter.

These waste baskets play a few risque messages to discourage littering.

A triumphant marble and bronze fountain depicting a 15th-century Hungarian king and his hunting party.

At night, this glittering musical tunnel draws skaters and photographers.

A somewhat mysterious biomedical museum housed inside a Spanish university.

A plaque bearing the names of those who dedicated themselves to protecting Budapest's Jewish population during World War II.

The geographical center of Budapest is marked with a 10-foot-tall stylized zero.

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

You can spot this teeny tiny stained-glass window from the Bonifacius bridge.

Sometimes called the Banksy of Madrid, Muelle was a pioneer of street art in the Spanish city.

The compass on its front was a handy tool for 17th-century merchants who needed to know the direction of the wind.

This fairytale castle was built as a show of power but was nearly torn down thanks to its history of torture.

Site of the first radio and telephone broadcasting companies in Copenhagen.

Climb to the top of its spiral spire for spectacular views of Copenhagen.

Danish tourist destination well known for open stalls where vendors sell marijuana on the street.

The de facto symbol of Copenhagen is this bronze fairytale which cannot seem to keep its head for very long.

The old observatory in Copenhagen has a spiral corridor used as a racetrack.

Beneath Denmark's Højbro bridge, a bronze merman and his seven sons forever mourn for the mother and wife who left them for land.

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

Swedish skyscraper with a 90° twist.

An ultra-modern diversity park in Denmark has turned an entire city block electric pink.

A concrete mushroom that divided Stockholm residents for nearly a century.

Creating this diorama spurred naturalist Carl Akeley to begin advocating to protect the apes.