This naturally heated mountainous creek has created a group of neon blue pools of potentially deadly boiling water.

The largest drain hole in the world.

The lowest point in North America is home to an undrinkable pool surrounded by fields of geometric salt flats.

Abandoned bridge hidden deep in the San Gabriel Mountains.

Finale of "William Tell Overture" can be heard as drivers pass over grooves in the road.

An unfortunate geological resemblance to Satan has labeled this Pasadena gorge as a passage to the underworld.

This abandoned Navy base was transformed into an off-grid alternative living community for thousands of people.

The largest permanent Monopoly board makes one of the longest games even bigger.

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

Once thought to be the oldest living tree in the world, Methuselah was germinated before the Egyptian pyramids were built.

A 300-ship graveyard, with a few still visible at low tide.

The now-abandoned tunnels were built for the transcontinental railroad on the route where the first wagon train entered California.

Visible below the waves are memorials to the city's Gold Rush dead.

The randomness of this wall of lava lamps helps encrypt up to 10 percent of the internet.

Eons old volcanic activity created one of the most stunning rock formations in the United States.

Aqueducts have dramatically changed this old lake, now home to tufa towers and its very own species of tiny brine shrimp.

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

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

The one-time watch house for incoming ships at the Golden Gate now stands abandoned and hidden in trees.

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

A hotel and restaurant serving as the mecca of kitsch.

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

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

A walk-in working camera obscura produces 360-degree live images of the San Francisco coast.