The world's longest known cave system.

Four hundred granite steps were built into this massive rock by the National Park Service.

The lighthouse central to the 1980s horror classic "The Fog" is, in fact, located in one of the foggiest areas of the Pacific Coast.

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

This rail trail culminates in a three-mile land bridge only accessible to cyclists and pedestrians.

Known as one of the most climbed mountains in the world, this barren peak is permanently bald thanks to an anti-wolf fire.

The national park was once a plantation estate.

This harrowing climb along West Virginia's jagged spires is one of the only Via Ferrata on America's east coast.

Chase waterfalls, hiking trails and more.

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

Oldest existing wire suspension bridge in the United States.

A farm in New Jersey grew a most unusual crop for AT&T's testing purposes.

Surprisingly aquamarine waters fill deep lakes formed at the end of the last ice age.

Beautiful views of the surrounding hills and birds of prey can be found at this sanctuary.

In use from 1742 to 1910, only flat headstones were allowed in this cemetery.

This elaborate towering structure was once famed for its revolutionary height.

An eccentric priest's tribute to George Washington, this chapel tells the story of the American Revolution.

Home to the deepest rift anywhere on Earth.

The only road through the heart of Glacier National Park.

Experience the wonders of a pristine night sky in this landscape free from light pollution.

The largest outdoor art gallery in the Northwest United States.

A little-known hot spring haven right below the highway.

This mesmerizing and surreal landscape features intricate patterns of white and red sandstone.

The unusual patterns in this rock formation result from two distinct modes of weathering.