This geothermal hot spring hides beneath a slowly growing mineral dome.

A particularly creepy abandoned hospital that sparks interest for lovers of the supernatural.

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

Frank Lloyd Wright's most iconic home dangles over a Pennsylvania waterfall.

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

Rustic natural hot springs in the deciduous rain forest.

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

A mysterious castle built as a monument to lost love.

A celebration of capitalism in Midtown.

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

An acoustic anomaly with a mysterious cause.

Seemingly grown on some other world, these New Mexico rock formations look like a disused science fiction set.

Where beautiful signs live on forever.

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

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

One person's lost luggage is another person's treasure.

Possibly the most beautiful carillon in the world, set atop Iron Mountain in Florida.

Hollywood's most famous landmark, the "temporary" sign that has stood for decades longer than intended.

The only swimming pool listed on the National Register of Historic Places is emptied and refilled each day with naturally filtered water.

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

A "gravitational anomaly" located in the redwood forests just outside of Santa Cruz, California.

Here, at the "world's longest art gallery," you'll find forty miles of ancient petroglyphs and pictographs.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

This secluded aqua waterfall in the Grand Canyon is the perfect swimming hole, and the Havasupai tribe's fiercely protected natural wonder.