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

An underground mansion with fruit-bearing trees and grapes growing beneath the surface of central California.

This semi-secret garden in south Seattle emulates a traditional Japanese garden using the plants of the Pacific Northwest.

A whimsical village of unique treehouses resides in a Washington forest.

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

The seawater playground of gilded-era San Francisco burned to the ground in 1966.

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

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

This strange seaside tower got its name from a wealthy eccentric who would hide coins among its stones.

If drivers cross the rumble strip on this stretch of Route 66 at just the right speed it plays "America the Beautiful."

Behind this beachfront shop lies a spectacular, colorful sea cave with an equally colorful past.

It's not hard to see why the historic Peabody Conservatory of Music's library has been described as a "cathedral of books."

The "Seinfeld" diner.

The largest self-built castle in the U.S., six decades in the making.

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

One of the world's oldest and most massive living organisms is a grove of quaking aspens.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

A modernist landscape of water and sci-fi concrete.

The longest continuous lava tube in the continental U.S. offers 2.5 miles of dark explorations for the adventurous.

The ghostly remains of an accidental sea.

This knobby, drooping New Orleans oak is a favorite place both for climbing and for meeting giraffes.

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

These delicate buggers are some of the rarest fossils that have bubbled up from the Tar Pits.

One of the oldest used bookstores in the U.S. has been selling antiquarian treasures since 1825.