A curious carving hides on a marble column in the Mosque-Cathedral of Córdoba.

A house covered entirely with shells.

This 47-story "M" needed 20 years to be completed

An abandoned socialist utopia built in the late 19th century.

An enchanting landscape of ancient sandstone structures eroded into otherworldly shapes.

This abandoned, turn-of-the-century astronomy hub is now the subject of more photographs than it ever took.

This massive fiberglass Gulliver turns every visitor into a Lilliputian.

Vibrant street art created with mixed media.

Of the many chalices in the running for the Holy Grail, this one in Valencia Cathedral sure looks the part.

This architectural oddity is an oasis of green on the outskirts of Valencia.

Bacteria and algae give the salty water its bubblegum hue.

Haunted tuberculosis hospital built by the patients.

Translating as "The Jump of the Girlfriend," this stunning waterfall has a tragic legend behind it.

The streets of a sleepy Spanish town proudly exhibit some of the world's finest graffiti.

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

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

A beautiful but toxic fountain of mercury.

This cemetery features modernist statues as strange as its name.

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

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.

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

A stately palace has been converted into the world's largest cannabis museum.

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