A 300-yard long natural tunnel runs through a ridge deep in the Appalachian Mountains.

The only diamond mine in the world where you can keep what you find.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

This legendary urban waterfall creates a dazzling display of rainbows.

Rainbow-hued in the summer and crystalline in the winter, this salty lake has inspired battles, temples, and plenty of awe.

A medieval stronghold rising over the ruins of ancient Roman villas along Rome's southern coast.

A medieval fountain lined with 99 unique stone faces whose origins and meaning remain unknown.

The skulls and bones of thousands of soldiers line the walls of this small Italian chapel.

Sitting on an Italian hilltop is this surreal fortress built by the mad inventor of electrohomeopathy.

Gnarled canopies of pink and purple wildflowers arch over the trail to the summit.

Named after a bandit and the star of several Hollywood prehistoric landscapes, these sandstone formations are a historical part of the Los Angeles natural landscape.

Each year these high desert hills are absolutely covered with poppy flowers in a surreal show of nature.

A quiet and contemplative oasis in the middle of New York's bustle and riot.

Hidden in a high mountain cave, this hermitage dates back to the ninth century.

A factory director designed what was the world's longest suspension footbridge in 1923 so his employees could get to work safely.

Crossing this suspension bridge feels like walking through the sky, a fitting tribute to the head of the Apollo program.

The world's longest known cave system.

When ecosystems collide in the arid Southwest.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

The highest dunes in California are the most likely place in the area to hear the Singing Sands.

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

One day a year it is legal to jump off of this astoundingly tall bridge that spans an Appalachian gorge.

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

Sunset-colored dunes of volcanic ash make taking a poor photo impossible.