A popular tourist cave with a dark past.

"Only the devil could play golf here."

A sign at the end of the Santa Monica Pier marks the traditional end of the legendary American highway.

An optical illusion found amid a logged redwood forest.

The liveliest ghost town in the state.

This quirky roadside attraction dives into the many theories surrounding North America's most infamous hairy cryptid.

Life in this isolated, hilltop lighthouse was lonely, but it sure was lovely.

A desert ghost town—occupied for only 12 years—was once home to more than 500 silver mines.

One of the most unusual geological features, recognizable from a dozen hit movies.

An extensive collection of ancient Egyptian artifacts and mummies.

Once strictly off-limits, this lower level housing curious and priceless vehicles of the Petersen Automotive Museum is now open to the public.

Commonly referred to as the most photographed Victorian home in the United States.

One of the oldest reform schools in the United States, home to wayward boys such as Merle Haggard, now abandoned.

An overlooked and unassuming engineering marvel.

Acres of natural wonders left behind by a socialite-turned-gardener.

Hundreds of trees made from glass bottles make up this forest on Route 66.

The unbelievably opulent home built for an infamous newspaperman.

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

These millipedes glow not out of attraction, but as a not-too-subtle warning.

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

San Francisco Bay's ghost town.

San Francisco's urban bison herd has persisted in the face of extinction, development, and disease.

California's own medieval Italian castle, authentic down to the 300-year-old iron maiden in the dungeon.

Standing in a state of "arrested decay," this ghost town allows for a detailed peek into Gold Rush life in an unusually harsh climate.