The gondolas let you glimpse a bird's-eye view of one of the world's highest capital cities.

Ecuador's largest Incan ruins show evidence of sophisticated irrigation and diplomacy among the ancient builders.

These beautiful ruins deep in the Pennsylvania woods are thought to have been a ski lodge or a speakeasy, but no one really knows.

Series of storm drains connected to a dark urban legend.

The scuba diving training facility was named for the steam that rises from the cave's chimney.

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.

The first declared National Monument in the United States.

"Only the devil could play golf here."

Hell on Earth is actually a small town in Michigan where anyone can be mayor for a day.

This massive subterranean fissure is known as the "underground Grand Canyon."

A whimsical bridge adorned with decorative dragons.

An immersive environment that is part haunted house, part choose-your-own-adventure, and part jungle gym.

Setting this massive marionette aflame rids Santa Fe of doom and gloom for another year.

The entrance to this sinisterly named tunnel hides behind a Tim Hortons.

The striking and little-touristed ruins of an ancient city destroyed and rebuilt by the Aztecs.

This giant wooden treehouse within a sprawling garden has its own eatery.

The ghosts of Britain's telecommunication past sit rusting away in a small village in England.

Once a dumping spot, now a park with a kayak launch.

This large cave is a summer home to thousands of bats and has a rich history dating back to prehistoric times.

A collision of human error and natural geothermal pressure created this rainbow-colored geologic wonder.

A treasure trove of artifacts, books, and artwork from the "golden age" of exploration.

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.

Some call this eerie forest of crooked trees the "Bermuda Triangle of Romania."

Get past the gatekeeper's apartment and enter an elaborate hoax of a restaurant with a Masonic feel.