A remarkably well-preserved stage stop from the late 19th century in a remote part of Nevada.

A new kind of theme park for adults off the Las Vegas Strip.

A breathtaking 19th-century trail overlooks Lake Tahoe.

Many generations of travelers have passed through the steep, smooth walls of this canyon.

The historic “pink house on the hill” is an architectural gem that now serves as a center for water conservation.

At the time of its construction, this hydroelectric power plant was the largest in the world.

A tunnel with windows, so you don't miss out on the impressive views.

The Roman city was the birthplace of various emperors and is home to one of the empire's most impressive architectural feats.

These paved rills bring freshwater into Altstadt and could spell wedding bells for whoever stumbles into the waters.

This former sugarcane transport tunnel is now a portal to a lovely beach.

The United States's largest hand-dug well is topped with a state-of-the-art museum.

Eco-village hidden in the foothills of the Alps that created a massive system of psychedelic underground temples.

This castle has links to Portugal’s founding and struggles for independence.

The U.K.'s first underground railway line is now a lively thoroughfare for runners and cyclists.

This floating garden in the sky is straight out of a fairy tale, but the real thing is nothing short of magical.

Italian director Pier Paolo Pasolini fell in love with this lonely 13th-century tower while making his most famous film.

This military tunnel dates back to World War II and provides visitors with a little wartime adrenaline.

At the time of its completion, it was the tallest dam in the world.

Half-hidden by grassy slopes, this striking Spanish colonial fort is now a museum of underwater archaeology.

The commemorative stone column conceals a secret laboratory.

The strikingly modern structure stands out among the brick buildings speckling the Harvard Business School's campus.

This spectacular track has run continuously since 1882.

A rare example of this century-old British tank stands near the center of town in Ashford.

Wander among the abandoned ruins of this once-powerful medieval town.