The ghostly remains of what was once the world's richest copper mine.

The world's longest known cave system.

The longest living non-clonal organisms on Earth.

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

Water of undetermined depth has attracted rare fish and cult leaders alike.

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

Ten 25-foot-tall, beehive-shaped kilns, abandoned in Death Valley.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

The deepest lake in the United States, and once the site of epic destruction that lives on in legends.

A community of collapsing homes more than a mile out from the Florida coast.

A gothic palace of endless stalagmites and pseudoscorpions waits within one of the world's most beautiful caves.

Travelers leave tea kettles in a remote part of Death Valley as part of a mysterious, decades-old tradition.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

A surreal landscape where fanged rocks rise from the ground and the ocean feels like a great mystery.

A throwback train ride transports passengers through one of the lesser-known national parks in the country.

This winding road of 318 curves is a must-visit for (careful) motorcycle and sports car enthusiasts.

One man’s religious convictions led him to build this stone castle meant to withstand an apocalypse.

This building contains handprints that are well over a century old.

In one of America’s oldest mountain ranges, a long-awaited section of a scenic highway is now open to the public.

A recreation of the doomed ocean liner in the middle of the Smoky Mountains.

An abandoned town is hidden in Great Smoky Mountains National Park.

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

Four hundred granite steps were built into this massive rock by the National Park Service.

Quite simply the largest tree in the world (by volume).