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

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

The works of poetry's biggest names grace the walls of the city of Leiden, all carefully painted by hand.

A market built atop boats is one of the few floating holiday markets in Europe.

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

A public urinal so pretty, it was declared a national monument.

Three connected pink triangles memorialize persecuted gays and lesbians throughout history.

A Dutch passageway's artistic, aquatic-themed makeover pays tribute to the capital city's famed waterways.

A beautifully eclectic mix of architectural styles.

This historic Amsterdam bar used to accept sailor's monkeys as payment.

This 22-floor tower's Skydeck offers panoramic views of Amsterdam.

An Amsterdam street lined with antique shops each one dedicated to a different obscure collection.

The world's only museum devoted to the wonders of fluorescence.

The now-overgrown beach resort was once frequented by Yugoslav military elite.

This oddly beautiful water cistern is a techno-temple to the wet stuff and a multimedia masterpiece.

A collection of old neon signs from all over Poland line a secluded courtyard.

This exclusive resort has completely covered a tiny Balkan island in a 5-star warren of guest rooms.

These historic defenses ensured the city within would survive hundreds of years of occupations, sieges, and invasions.

This sprawling concrete suburb of Kraków was designed by the Soviet Union as the model proletarian city.

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

Destroyed Serbian army headquarters sits half crumbled in a largely revitalized Belgrade.

Nikola Tesla's ashes are held in a golden sphere, surrounded by his works.

Where commuters walk through remnants of an ancient Greek necropolis.

A sharp sculpture made of thousands of pieces of jagged glass.