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

These abandoned country fairgrounds are filled with replicas of Spanish monuments.

Not far from Madrid, a set of perfectly preserved trenches date back to the Spanish Civil War.

A reproduction of the famous prehistoric cave paintings is hidden underground at the National Archaeological Museum.

Stuck in the middle of a modern Madrid city block are the remains of a 19th century sports complex.

This postmodern apartment block was designed to be a vertical neighborhood.

Just like in Hollywood, Madrid has also a forgotten walk of fame.

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

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

Among the oldest structures in Madrid, these Moorish walls once guarded the medieval city of Mayrit.

This lucky bronze frog was gifted to Madrid by a casino.

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

The only urban monument in the world designed by the great surrealist painter Salvador Dalí.

A whimsical brother of the nearby Fallen Angel statue takes the falling part quite literally.

Abandoned for decades, trains still pass through the now-restored remains of one of Madrid's first metro stations.

The oldest restaurant in the world is this old-world Spanish eatery, still known for its suckling pig.

An unusual vending machine designed to support mourners during funeral ceremonies at Zurich's largest cemetery.

This small museum displays a collection of outsider art and scale models of past "treatments" for mental illness.

Museum of science fiction, utopias, and extraordinary journeys of the mind.

Traversing steep Alpine slopes, this engineering marvel is one of the longest and highest funiculars in the world.

One hundred years ago this small house in downtown Zürich became the birthplace of the Dada movement.

This historic covered bridge contains a series of macabre paintings that communicate one thing: everyone dies.

The steepest classic funicular in the world glides along a dizzying incline.

A breathtaking bridge that crosses a vast gorge over a river's torrents, and has a tale of a devil architect attached.