Hanging over one of Japan's "hidden valleys," these vine bridges must be remade every three years.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

A museum dedicated to the Spanish occult in a town that was terrorized by the Inquisition.

What was once the largest mine in North America has left behind a hollow hill filled with bright blue waters.

A tiny microvalley etched into the side of Knocknarea Mountain hides another world.

The remote outlaw hideout of Jesse James, Butch Cassidy, and the Sundance Kid.

This huge pile of volcanic boulders hides a stunning network of secret grottoes.

For two weeks every June, fireflies in the Smoky Mountains perform an astonishing light show.

Staves, storm-calling, and of course, necropants.

The 1936 Summer Olympics site is a crumbling remnant of sportsmanship and a history its host country would like to forget.

Buildings from the fictional planet of Tatooine still litter the Tunisian desert.

Mother Nature outdoes herself with this stunningly beautiful set of caves carved into marble.

A swing to dangle you off the very edge.

The fairy tale castle of the "fairy-tale king."

An ancient capital city that dates back 3,000 years old and harbors many surprises.

A toxic ghost town sitting atop a massive coal fire.

A fiery crater has been burning in the Karakum Desert since 1971.

Most-visited and most-photographed slot canyon in the American Southwest.

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

The neon signs from Las Vegas' past find their final resting place at this unusual graveyard.

On the Oregon coast there is a natural hole that seems to be draining the sea.

The intricate stonework of Machu Picchu serves as a testament to Incan engineers.

An emerald-green grotto just a short trip from Austin.

The mysterious, fantastical woodland inspiration for "The Lord of the Rings."