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

For centuries, the largest Arab bathhouse in Spain was hidden under a palace.

Built thousands of years ago, this wall is still part of the urban layout of this village.

Meant to resemble a massive tree, the building is the best example of Spanish organicist architecture in Madrid.

A neighborhood represented by an apparent geocentric and flat-earth model of the Solar System is hidden in the subway of Madrid.

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

In the fictional world of Kcymaerxthaere, celestial wonders marked a portal to a powerful route of travel at this site in Madrid, Spain.

The remains of the second-oldest zoo in Europe can be seen within these library gardens.

This sweet-toothed bear searching for snacks has been a symbol of Madrid for decades.

This macabre masterpiece of a mural is one of Francisco Goya's "Black Paintings."

An unexpected homage to 90s celebrities hidden in a corner of Ibiza.

One of the best examples of the modernist movement in Madrid.

An ancient Egyptian temple in the middle of Madrid, Spain.

An ode to the famous Las Vegas signage.

Housed in a stunning Victorian building, this museum has the largest exhibition of knives, blades, penknives, and scissors in Spain.

The oldest building in Madrid.

This sculpture of a rider on horseback once crowned the tomb of an Iberian aristocrat.

This uniquely shaped 17th-century structure comes alive in early September.

Strange masks and obscure costumes are housed in this old Madrid corrala.

This grand gate once marked the entrance to a military barracks.

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.

Touching the iron railings of Tarragona's balcony to the Mediterranean is said to bring good luck.

Madrid's romantically ornate crystal palace has been offering shelter to plants and art for over a century.

Three bridges and one giant canyon make up this fantastic Spanish settlement.