An overlooked and unassuming engineering marvel.

Built from one couple’s vast personal collection, this free museum showcases a century’s worth of state-sponsored agitprop.

Special tunnels built so that frogs won't be killed when crossing the highway.

The largest drain hole in the world.

This graffiti-covered bridge is the quintessential vision of a place for disillusioned youth to escape the complexities of burgeoning adulthood.

Seven ceramic sculptures are scattered around this California college campus.

Outsider art or homage to aliens?

If you dial the number in this abandoned office window "Sam Spade’s" secretary will ask you to leave a message.

The only parking meter in the entire town, it is surrounded by 100 free spaces.

Millions of years of oxidation make a drive down this winding Death Valley road surprisingly colorful.

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

A sparse, solitary sequoia still stands as a living tribute to the famous conservationist who planted it—but it's dying.

Happy harbor seals frolic and snooze on this warm, sandy stretch of coast.

A cozy bookstore is tucked within an old gold mine shaft beneath the cafe and ice cream shop.

These falls, sometimes called the "Niagara of the West," still put on a good show at the right time of year.

A large lava tube that can be walked through with no special equipment.

A tiny survivor of the Donner Party disaster.

At night, a grove of towering redwood trees growing through the pavement block out all light from the so-called “Dark Park” of Madrone Avenue.

One man's love of natural beauty led to the creation of this hidden granite monument.

Across Ring Mountain is a vast collection of Native American petroglyphs unique to the region.

The only bridge in the United States where BASE jumping is legal without a permit year-round.

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

One of nature's most well-scheduled phenomenons resides in Wyoming's Yellowstone National Park.

A beautiful geyser under environmental threat.