The hidden ruins of an old hydroelectric plant reclaimed by nature.

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

Spanish architects used seized Muslim gravestones to rebuild parts of the fortress.

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

Spain's unique Mosque-Cathedral has been a place of worship for both Muslims and Christians throughout its history.

Bold black and white motifs of life and death add a dramatic flair to this 17th-century crypt.

This former charity hospital for elderly clergy houses some of Seville’s most treasured paintings.

The final resting place of the great navigator, or maybe his brother.

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

An underground paleo-Christian burial site composed of the remains of several cemeteries and Basilicas.

A labyrinth of ancient tunnels hidden below the city holds the ruins of 2,500 years of history.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

This abandoned subway station can still be seen on regular commuter trips.

An abandoned dollhouse factory.

A large boulder marks the place where the island of Manhattan was purportedly "sold" to the Dutch.

This hidden oasis features a stunning view of the Hudson River and the Palisades from a castle-like museum.

You must take the A train... to the last active cemetery in Manhattan.

New York City's only radical feminist independent bookstore.

This enormous banquet-themed artwork honors over 1,000 notable women throughout history.

This stone gatehouse was once the entrance to a historic mountain resort, and it had a cameo in a cheesy cult horror movie.

This once-grand marvel of engineering is now 41 miles of scenic hiking trail.

Every year model trains zip through a miniature New York City that's now 150 landmarks strong.

The mummified relics of an American missionary.

Little Red Lighthouse under the George Washington Bridge.