An abandoned Byzantine fortress and notorious prison.

The world's largest indoor go-kart racetrack is hiding in Connecticut.

A 300-foot-long Cold War submarine floats in a Chilean River as a maritime museum.

The world's largest wooden trestle stretches across this desert canyon in Anza-Borrego Desert State Park.

The world's fifth tallest waterfall is a spectacular silver chute of water that cuts through the cloud forest in northern Peru.

With nearly double the depth of the Grand Canyon, this Peruvian canyon is one of the deepest in the world.

Etched into a dry lake bed, this massive directional indicator is accurate without magnets.

A 1,500-year-old, 3-story subterranean city where ancient Persians took refuge in times of war.

This futuristically sylvan church is a glass-enclosed marvel of modern architecture.

The skeletal white beams stand as a monument to religious dissent.

The nearly 200-year-old folly has a secret spiral staircase hidden in one of its pillars.

An isolated 17th-century chapel on a remarkable site once dedicated to Celtic sun worship.

This small oxbow lake has rare giant river otters and some Seussian-sounding birds.

One of the most remote lodges in the Amazon offers rare wildlife encounters and undisturbed views of the Peruvian rainforest.

A 6th-century stone lies at the site of the mythical battle waged between King Arthur and his nemesis Mordred.

Stunning ruins of what was once the center of one of the greatest empires in East Africa.

A remarkably well preserved tower dating all the way back to the Iron Age.

An imposing Omani fortress surrounded by date palm trees.

The only Frank Lloyd Wright-designed structure in the architect's hometown.

A medieval church built up to defend its village.

This fairy-tale, neo-Gothic church in the Azores is a world of magical realism.

Stroll through a wonderland of stupendous moss-covered trees.

More than half of this Indian palace is drowned but it looks all the more spectacular for it.

This natural wonder drops 16 stories straight down through rare flora and streaming waterfalls.