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

Hundreds of glow-in-the-dark objects light up a museum in a historic zinc mine.

Wild lights and sound effects turn a walk through some caves into an eye-popping 1960s tourist attraction.

A clear blue swimming hole with hidden caves, still unexplored.

An essential stop before plundering, BYO Cutlass.

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

See massive fossils that are over 200 million years old in northeastern Arizona.

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

One of the most scenic stretches of road in America winds between some of the country's oldest trees.

Breathtakingly blue walls shimmer inside the "Glacier Behind the Town."

Giant, natural amphitheaters made of delicate geological formations called "hoodoos."

An abandoned stretch of highway, deteriorating next to the operational one.

This natural wonder drops 16 stories straight down through rare flora and streaming waterfalls.

The scuba diving training facility was named for the steam that rises from the cave's chimney.

Carved by a waterfall in a hard-to-reach rock formation, this heart-shaped rock has inspired romantics for decades.

Quite simply the largest tree in the world (by volume).

In the middle of an extremely unforgiving and desolate high desert is the most secret military facility in the world.

A sacred site for Native Americans surveyed by George Washington and owned by both King George III and Thomas Jefferson.

This naturally-sourced hot spring is now home to a clothing-optional resort.

A museum dedicated to the alleged Roswell Incident.

An acoustic anomaly with a mysterious cause.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

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

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."