Relics of the 1894 Midwinter Exposition continue to delight visitors today.

The last remaining relic of San Francisco's glittering 1915 Panama Pacific Exposition.

A modern mechanical planetary system, part of a 10,000 year clock.

Carnivorous plants, medieval aphrodisiacs, and the largest original wood structure glass conservatory in the western hemisphere.

This concrete tangle of square pipes has stood as a proud thorn in the city's side since the '70s.

Since 1973, this block has been home to the most concentrated collection of murals in San Francisco.

Not merely a museum – but a whirring powerhouse that offers a subterranean peek into the heart and soul of cable car operations.

This one-block alleyway is stuffed with street art that is colorful, cultural, and intensely political.

The former private quarters and office of Dr. Sigmund Freud now hosts a museum housing the works of the founding father of psychoanalysis.

Berlin's old airport.

On the Spree bank, discover one of the last reminders of a symbolic wall that divided, and was torn down by the people.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

Elevated freight railway turned wildly successful urban park.

One of only two commuter aerial tramways in the United States.

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

Mysterious 500-year-old tapestries depict a unicorn hunt.

The mummified relics of an American missionary.

The oldest surviving bridge in New York City, which reopened to pedestrians in 2015.

The first "Hall of Fame" in America was designed by legendary Gilded Age architect Stanford White for what was then the NYU uptown campus.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

Ancient catacombs form the foundation for this Rococo orgy of a church.

The stunning interior of this Gothic church is covered in ornate gold details.

Elaborate tile work in this railway station tells the story of Portugal.