It was once the base for a series of domestic terror attacks.

One of the most influential presidents in U.S. history wanted only this plain, elegant monument as his lasting memorial.

A much-maligned monument to teetotalism.

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

This unassuming passageway played a key role in one of the most important events in U.S. history.

The house where John Wilkes Booth conspired with his co-conspirators.

The unique traffic pattern named for an influential urban planner is also known as the Pedestrian Scramble.

Go take a picture with the inventor of the daguerreotype photographic process.

This beloved marketplace mascot poops money and grants good luck.

This charming colonial alleyway is one of the oldest continuously used residential streets in the U.S.

This generously endowed statue once stood guard outside a Roman home.

An eerie diorama that captures the majestic nature of a few prehistoric-looking beasts.

This beautiful Brooklyn monument over a crypt memorializes a grim and largely unknown story from the American Revolution.

The 2,000-year-old Roman columns are hidden within Barcelona's Gothic Quarter.

A beautiful but toxic fountain of mercury.

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

An early 20th-century bullring converted into a modern shopping center.

The highest rapid transit station in the world.

A lush indoor jungle fills this bustling Madrid transportation hub.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

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."

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

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