Stunning Roman aqueduct used for 1900 years and still standing.

Abandoned waterpark turned counter-culture mecca.

This whimsical winery by Antoni Gaudí looks ripped from the pages of a fairytale.

This chest hospital with a dark, haunted past serves as a fitting set for horror films and a paradise for ghost hunters.

A Spanish forest is filled with mysterious stone carvings.

Cursed swimming pool left abandoned is now a favorite of filmmakers and ghost hunters.

A gravity-defying "devil's bridge" that has a surprising architectural feature for its stability.

This imposing modern citadel started out as a home renovation project.

An architect transformed this abandoned cement factory into his castle-like workshop.

A surrealist labyrinth and museum of contemporary sculptures.

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

A once grand hotel now sits eerily abandoned in the Catalan countryside outside Barcelona.

The former 1920s mansion of a prominent Catalan developer was used as the Soviet Embassy during the Spanish Civil War, and there is still a bunker below the garden.

This mansion oasis contains gardens, sculptures, and fountains just off the busy Plaça Kennedy in Sant Gervasi.

Barcelona's only remaining tram system takes riders to the Tibidabo funicular.

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

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 cemetery features modernist statues as strange as its name.

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

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.

The studio of Catalonia's most famous theatrical designer remains exactly as he left it.

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