Hot springs monkey spa in the middle of Hell's Valley.

One man has carved a number of natural New Mexico caves into psychedelic sandstone temples.

Under the right circumstances, this waterfall in Yosemite briefly turns a luminescent fiery orange.

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

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

Crystal clear lake with a shoreline of travertine located in a Colorado canyon.

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

The installation’s official name, “You Who Are Getting Obliterated in the Dancing Swarm of Fireflies,” says it all.

A bizarre house filled with an astounding array of collections.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

A church of bones, decorated with 40,000 human skeletons.

An enormous, inside-out glass globe built in 1935.

The history of occult science is turned into a creepshow at this lurid Prague tourist attraction.

These old stone ruins in the Oregon wilderness were once bathrooms and are steeped in legends of murder.

An abandoned cemetery lies in ruins as the surrounding forest swallows it whole.

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

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

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

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

Bring your own cardboard to the slippery slopes of concrete hidden in a neighborhood park.

The sound of swaying stalks in this stunning grove has been named a governmentally recognized sound.

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

An easily overlooked memorial to a Ukrainian famine-genocide that killed over 4 million people.

A historic estate packed with George Washington's heirlooms, and its own nuclear bunker.