A breathtaking and biodiverse wilderness in the mountain setting of Ernest Hemingway's "For Whom the Bell Tolls."

A magnificent, long-abandoned castle built in the wake of the reconquest of Spain.

This 18th-century project to build the world's tallest gravity dam was never completed.

An exact replica of a colossal Olmec head sits atop a pyramid within a Madrid traffic circle.

A huge cathedral single-handedly constructed by one eccentric monk.

A subterranean relic of the Spanish Civil War hides below this picturesque park.

This technological marvel is one of the world's first 3D-printed bridges.

A beautiful little castle with a rich history now home to the Archives of the Spanish Air Force.

A model solar system adds a celestial touch to this suburban park.

A historic castle that served as a backdrop to part of an elaborate extraterrestrial hoax.

The magic of Spanish aviation housed under one roof.

An open-air sculpture museum in a park in Alcorcón.

Many miles south of Loch Ness, a similarly-named sea monster stands at the center of a roundabout.

An iconic photograph from the Spanish Civil War saved this shrapnel-scarred historic house from destruction.

This amazing abuela became a diehard metal fan late in life and an icon of Madrid's '80s rock scene.

Nicknamed the "Spirit of Paul Klee," this colorful apartment building features an array of multicolored panels.

The oldest building in Madrid.

Infamous and now demolished panopticon prison built by its former inhabitants.

This Art Nouveau gate still stands at the former entrance of a 20th-century Spanish writer's colony.

Built to celebrate the glory of a new queen, this forgotten monument has moved around Madrid three times, reflecting 200 years of political whims and city redevelopment.

This cuddly-looking statue symbolizes the bond between Spain and China.

This phone booth was recreated to honor "La cabina," considered the best horror film in the history of Spanish television.

The little church's beautifully frescoed ceiling has earned it the nickname “the Sistine Chapel of Madrid.”

A window into a long-lost world, these colorful tiles advertise a long-defunct range of purgative teas, harmless smokables, and diarrhea cures.