The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

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

Possibly the oldest church in Barcelona, this basilica has its pagan and Christian mythologies all mixed up.

One of the most photographed buildings in a city known for its Modernista architecture is an abandoned squat.

A former steam-powered mill from the 1800s is now an industrial park with a giant steel dragon slide.

A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

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

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.

One of Europe's largest supercomputers is housed inside of a disused chapel.

Bask in the 19th century grandeur of an eccentric Freemason millionaire's private gardens.

Turntable anonymously received orphans, alms, and groceries.

Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

Week-long block party becomes a competition for the best decorated street.

Mountain where Jesus was first tempted by the Devil.

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

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

This cemetery features modernist statues as strange as its name.

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

A beautiful but toxic fountain of mercury.

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

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