The remains of a failed attempt at medieval nerdery are hidden deep in the woods of Virginia.

An underwater city for the dead.

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

Olfactory delights in San Francisco's Botanical Gardens.

Relics of the 1894 Midwinter Exposition continue to delight visitors today.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

Carnivorous plants, medieval aphrodisiacs, and the largest original wood structure glass conservatory in the western hemisphere.

One of the world's oldest and most massive living organisms is a grove of quaking aspens.

A beautiful geyser under environmental threat.

Get lost in this haunting fairytale art walk through a man-made eucalyptus grove.

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

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

An underground mansion with fruit-bearing trees and grapes growing beneath the surface of central California.

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

Enormous lake at the bottom of a unique cave system.

A Pythagorean funhouse that tries, successfully, to prove that math is the coolest thing ever.

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

A winding path built in secret on the edge of the continent.

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

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

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.

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

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