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

A giant Troll lurks under one of Seattle's oldest bridges.

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

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

A bizarre house filled with an astounding array of collections.

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.

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

Remants of foundations, streets, and streetcar tracks inhabit the cliffs where a landslide occurred in 1929.

This abandoned subway station beneath the Waldorf-Astoria hotel is allegedly used to secretly transport presidents.

Dramatic river bend surrounds a natural red-rocked pedestal.

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

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.

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

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

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

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

A crumbling hospital from the 1850s on Roosevelt Island.

Rippling sand dunes frozen in the Arizona rock.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.

These eerie outliers of the lightning bug family glow a mysterious blue color.

This super steep hike ascends 2,000 feet in less than a mile.

The world's largest carnivore sanctuary is home to over 450 meat-eating rescues.

Despite being one of the most photographed vistas in the Rockies these twin peaks are rightfully known as the "Deadly Bells."