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

San Franciscans leave gifts and messages for the magical beings that live behind the tiny, mysterious door installed on a tree in Golden Gate Park.

The L.A. Zoo has a secret garden of rare bootleg cycads, a palm specimen dating back 280 million years.

The abandoned personal amusement park of the King of Pop.

The biggest pinball arcade in the world has over 600 pinball machines, and 300 arcade machines.

The neighborhood shop is a sort of tiny cactus museum full of exotic specimens you can take home.

One of the last free public hot springs is decorated with hippie art.

World's oldest operating science fiction and fantasy club, once home to Ray Bradbury and L. Ron Hubbard.

San Francisco Bay's ghost town.

The oldest burial ground in the city, final resting place of city founders, Ohlone natives and murderers alike.

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

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

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

San Diego's most historic and haunted home.

A storybook European village in Berkeley.

Costumed elves and mountain bikers co-exist peacefully at this abandoned Christmas-themed adventure park.

One of the ghostly stops along Route 66.

An extraordinarily ornate museum in San Diego holds wondrous anthropological treasures.

This ultra-modern home clings to the slope of the Hollywood Hills on a precarious stilt.

The "Fun Spot of the Desert" is now a haunting ruin, and a reminder that putting a water park in a desert is a bad idea.

Travelers exchange letters with woodland creatures at this mini post office.

The site of murders and Satanic cult gatherings.

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

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