The longest living non-clonal organisms on Earth.

Dyed by iron oxide over centuries, these sandstone rocks rise thousands of feet into the sky.

The now-abandoned tunnels were built for the transcontinental railroad on the route where the first wagon train entered California.

148 feet long and in the middle of a verdant forest.

One of the largest-ever mental hospitals now sits abandoned, surrounded by 25,000 unmarked graves.

Despite being one of the most photographed vistas in the Rockies these twin peaks are rightfully known as the "Deadly Bells."

Sandstone rock formations that look like they belong on the cover of a progressive rock album.

The eerie remnants of an ancient forest were hidden under the sand for centuries.

A half-mile long and three stories high, this bridge over the Des Moines River Valley mimics a descent into a mine shaft.

Visit this playground of waterfalls, caves and sinkholes.

Read between the lines of the subway map to find the hidden abandoned Civil War fort.

These beautiful ruins deep in the Pennsylvania woods are thought to have been a ski lodge or a speakeasy, but no one really knows.

Eons old volcanic activity created one of the most stunning rock formations in the United States.

In a 345-million-year-old cave that's 200 feet underground, dinner awaits.

Aqueducts have dramatically changed this old lake, now home to tufa towers and its very own species of tiny brine shrimp.

This Big Sur waterfall drops 80 feet directly into the Pacific Ocean, and inspired the hillside house up top.

Stripes of flowers bloom each spring in a 50 acre rainbow of color.

This lake in the Cascades lives up to its name, disappearing down a hole every spring.

Trails through lava-carved tube-caves display sparkling bacteria and a rich history.

Sail through this subterranean show cave that is home to a legend that would go on to name nearly everything around it.

A tiny red pebble marks what may be the quietest outdoor spot in the United States.

Canyon walls shrouded in ferns.

The highest bridge in America was built for an almost unnervingly small amount of money.

A 300-yard long natural tunnel runs through a ridge deep in the Appalachian Mountains.