The United States Capitol's former columns still stand.

Enormous lake at the bottom of a unique cave system.

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

A toxic ghost town sitting atop a massive coal fire.

A collection of oddities including Dr. Kevorkian's suicide device, the Thanatron.

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

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 Boston medical museum features the skull of the famous medical case of Phineas Gage.

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

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

Manhattan’s Battery Park has a whimsical carousel full of spinning, glowing fish.

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

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

Dramatic river bend surrounds a natural red-rocked pedestal.

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

The neon signs from Las Vegas' past find their final resting place at this unusual graveyard.

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

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

A crumbling hospital from the 1850s on Roosevelt Island.

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

Rippling sand dunes frozen in the Arizona rock.