It would take 35 firetrucks to fill this enormous glacial pothole.

This lush forest valley was once mined for lumber to the extent that it was once nicknamed "The Pennsylvania Desert."

The largest university building in the West is a gothic masterpiece containing dozens of theme rooms based on different countries.

An indoor miniature village and labor of love for Laurence Geiringer, a model railroad enthusiast.

Frank Lloyd Wright's most iconic home dangles over a Pennsylvania waterfall.

A toxic ghost town sitting atop a massive coal fire.

South Dakota's oldest operating brewery is housed inside a historic firehouse.

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

Obscure Freemasons still live in D.C.’s largest private residence.

Home to items never before seen by the public.

A model of a dinosaur that was named for Andrew Carnegie stands outside the museum that also bears his name.

Odd outsider art installations surround a Gold Rush-era ghost town.

The United States’s oldest funicular railway glides up and down a steep Pittsburgh street.

The world's longest known cave system.

The world's largest mountain carving could fit all of Mount Rushmore inside it many times over.

Macabre headstones carved with winged skulls, dancing skeletons, and pithy reminders of impending death.

Watch the newest land on the planet form before your eyes.

A popular day's outing in Bovington consists of watching military tank driving practice.

A beautiful geyser under environmental threat.

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

In which a local geological marvel becomes a quaint roadside attraction.

The first declared National Monument in the United States.

An almost life-sized elephant named Ms. Ellie greets visitors at this jumbo-themed museum.

Earth's tallest volcano is sacred to Native Hawaiians, and home to a dozen world-class observatories.