"Dark Sky Park" is heaven on Earth for astronomers, one of the rare U.S. locations with no artificial light pollution.

North America’s largest collection of horological devices and home to a colossal clock with a dizzying array of features.

This little-known collection holds everything from "Dracula" notes, to the manuscript of "Ulysses," to the forged works of Shakespeare.

The oldest farmer's market in America is so ancient it was approved by the King of England.

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

The only way to see Pittsburgh is from the top of this lookout point, just like the ancient members of the native peoples did.

Contrary to what one might expect, ice forms inside this small cavern during the summer and melts during the winter.

A preserved 18th century homestead in Western Pennsylvania marks the spot where the Whiskey Rebellion began.

A planned settlement in Pennsylvania once housed the aristocratic refugees of the French Revolution.

Home to the largest urban bat colony in North America, estimated at 1.5 million bats.

The only international border marker within the United States.

The last holdout of a pre-Civil War rebel who took the matter of slavery into his own hands.

In the basement of the U.S. Capitol Building is a hidden storage room full of ornate floor tiles leftover from the 1850s.

This nature center has one of the largest collections of native raptors in the Pacific Northwest.

The largest earthwork effigy in the world.

Over 50 historic windmills whir away at this outdoor museum.

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

A museum devoted entirely to the rattlesnakes and snake-related art.

On the side of a remote mountain, a stone face bearing an inscription of mysterious origin.

A multi-storied adobe complex has been inhabited for more than a thousand years.

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

This former Mormon settlement is reemerging from the receding waters of Lake Mead.

Brightly colored 30-foot-tall totems light up the desert sky just outside Las Vegas.

The longest living non-clonal organisms on Earth.