Step inside the first house designed by Catalan architect Antoni Gaudí, considered to be one of the first Art Nouveau buildings.

A beautiful but toxic fountain of mercury.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

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

This semi-secret storybook hedge maze is also the oldest garden in the city.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

Over a century old, this restored Victorian building is surrounded by a lush garden filled with rare palms.

Furniture tries to escape an abandoned building in San Francisco.

Europe's official "zero-level," the equator of elevation.

In the days before house numbers, these colorful signs held clues about various buildings' purposes.

This pirate-broadcasting-tower-turned-restaurant played a rebellious role in the history of Dutch television.

This large copper bolt represents the benchmark for measuring sea levels in most of Europe.

This unattributed sculpture in Amsterdam is hiding in plain sight.

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

Seven mini rowhouses fill the gap between 54 and 70 Westerstraat.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.

A beautifully eclectic mix of architectural styles.

Established in 1638 to battle the Black Death, Hortus Botanicus Amsterdam is a treasure trove of rare flora.

The world's first zoo for microbes collecting the horrible and wonderful things living on and around us.

A floating cat sanctuary on an Amsterdam canal.

Cat art as far as the eye can see.

Museum preserving torture methods from the past.

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