A huge musical instrument played by the ocean.

An artsy hidden staircase leads to breathtaking views of San Francisco.

A self-built castle made by a mysterious man.

Colorado's only true geyser is hidden within the San Juan National Forest.

Brightly colored 30-foot-tall totems light up the desert sky just outside Las Vegas.

A massive hydrovolcanic explosion left a half-mile wide crater in Death Valley.

A hard-to-reach oasis in a desolate corner of Death Valley National Park.

This desert oddity hides in plain sight thanks to a cartographic error and a desert explorer with a punny sense of humor.

The highest point in Nevada had to be decided by court order after California tried to claim it as their own.

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

Towering basalt columns, a creation of fire and ice.

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

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

Bits and pieces from the ill-fated Donner Party's winter cabins.

A breathtaking 19th-century trail overlooks Lake Tahoe.

Since 1973, this block has been home to the most concentrated collection of murals in San Francisco.

A tiny theater hidden in an alley plays a constant stream of short silent films for anyone willing to peer through the peephole.

Gold Rush-era tombstones line the park's paths.

The last remaining relic of San Francisco's glittering 1915 Panama Pacific Exposition.

One of few lasting examples of the brief octagon craze that developed into folly.

This one-block alleyway is stuffed with street art that is colorful, cultural, and intensely political.

Bring your own cardboard to the slippery slopes of concrete hidden in a neighborhood park.

Centuries of crashing waves carved out this small hole in the rock, which lights up at certain parts of the year.

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