A Bicycle Path in the Sky.

A raised boardwalk winds through a thicket of stunted, century-old trees no more than nine feet tall.

The world's largest wooden trestle stretches across this desert canyon in Anza-Borrego Desert State Park.

Sunset-colored dunes of volcanic ash make taking a poor photo impossible.

The unedited photograph called "Bliss" has graced the screens of over a billion computers.

A sign at the end of the Santa Monica Pier marks the traditional end of the legendary American highway.

A desert ghost town—occupied for only 12 years—was once home to more than 500 silver mines.

This rare example of a "tidefall" is a spectacular drop from the cliffs down onto the beach.

San Francisco's urban bison herd has persisted in the face of extinction, development, and disease.

One of the ghostly stops along Route 66.

Standing in a state of "arrested decay," this ghost town allows for a detailed peek into Gold Rush life in an unusually harsh climate.

An inconspicuous footbridge beloved by San Diego locals.

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

Towering basalt columns, a creation of fire and ice.

Island where motor vehicles are banned -- home to the only carless highway in the United States.

If you want to take a peek at Area 51, this is legally as close as you're going to get.

This road in the Great Smoky Mountains was supposed to assuage a displaced community, but ended up a $52 million dead end.

The Virginia farm where John Wilkes Booth met his grisly end is now largely forgotten.

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

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

Post office plaque commemorates local resistance to a cult invasion.

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

A roaring, awe-inspiring double cascade of icy water flows through woodland Oregon like something out of a Tolkien novel.

A mysterious monument meant to be a guide into "an Age of Reason" was destroyed after an apparent bombing.