The Pope’s secret escape route.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

2300-year-old Roman road connecting the empire.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

Barça football fans might see the insignia hidden in a church window as a divine sign.

A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

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

The oldest giants in Catalonia are now displayed in a 14th-century Gothic church.

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

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

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

Louisa May Alcott based “Little Women” on her experiences growing up in this house with her sisters.

This Niagara Falls tourist trap is a world bright with neon and curiosities that will inspire love, hate, or a mixture of both.

A Beaux-Arts triumph set to become Ford's innovation campus

These enduring murals depicting a distinctly Marxist tribute to capitalism could not even be defeated by McCarthyism.

Controversial tribute to the heavyweight champion boxer who grew up in Detroit.

The enormous 250-room Vanderbilt mansion conceals hidden doors and secret passageways.

The only royal palace on U.S. soil has been a territorial capitol, a military headquarters, and a prison for a queen.

This museum of Hawaiian and Polynesian culture is the legacy of the last descendant of the Kamehameha Dynasty.

An authentic replica of an Asian temple and garden hidden amongst the natural beauty of Hawai'i.

Race through the maze, get your name on the sign.

A dramatic, 360-degree recreation of Pickett's Charge in the Civil War.

FDR's Art Deco hospital tower was hopelessly inefficient.