An open-air "garden" of mural art that changes weekly.

On the wall of this medieval walkway, a symbol of the Spanish Inquisition.

This fountain was designed to honor the man who helped bring water to Barcelona.

This former Baroque palace on the historic Calle Montcada is a rare architectural gem and was once the meeting place of an aristocratic scholarly society.

Barça football fans might see the insignia hidden in a church window as a divine sign.

This home designed for chocolate magnate Antoni Amatller is an exquisite treasure-box of Catalan Modernism.

The 2,000-year-old Roman columns are hidden within Barcelona's Gothic Quarter.

Fantastic stories on a miniature railroad.

Resting in the middle of an Austrian river, this sci-fi "island" lets people cross in neon style.

Old ships and machinery fill a historic harbor in the city that's home to Europe's largest port.

The Netherlands' first car tunnel has an unusually rectangular shape.

A condensed piece of China floating in a Dutch harbor.

Science meets wall art to highlight the beauty of famous mathematical equations.

Only a few walls remain of the last church the Pilgrims used before they sailed to North America.

A massive explosion that leveled hundreds of buildings in the city of Leiden is remembered by a waterside plaque.

People have been placing babies on these lilies for photoshoots since the Victorian era.

A 'living museum' in Leiden, the oldest of its kind in the Netherlands.

An unassuming rod in the Netherlands was once the old standard unit of length for the entire Dutch empire.

A trio of red, white, and blue stones embedded in the streets of Leiden are markers of medieval territory and law.

This 11th-century castle sits so low you can't see it behind the surrounding buildings.

Portraits of musicians line Oude Binnenweg, the jazziest street in the city.

This unique sculpture proved invaluable when it saved a train from careening off the tracks.

A guitar mounted on a wall in Temple Bar honors the Irish musician.

This neon landmark has been posing this deadpan question to follicly-challenged Dubliners for over 50 years.