Enormous lake at the bottom of a unique cave system.

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

The only swimming pool listed on the National Register of Historic Places is emptied and refilled each day with naturally filtered water.

This massive stained-glass masterpiece is thought to be the largest Tiffany dome in existence.

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

One man's homage to the sun continues to grow like a glass fractal.

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

A roaring, awe-inspiring double cascade of icy water flows through woodland Oregon like something out of a Tolkien novel.

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.

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.

High on a hill overlooking Los Angeles lives a world famous, high power conical Tesla Coil.

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

This secluded aqua waterfall in the Grand Canyon is the perfect swimming hole, and the Havasupai tribe's fiercely protected natural wonder.

Wondrous sandstone hoodoos where Native Americans collected clay for pottery, 9,000 years ago.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

Dramatic river bend surrounds a natural red-rocked pedestal.

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

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

A tiny museum housed in a New York freight elevator specializes in the "overlooked, dismissed, or ignored."

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

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

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