Each winter this underground cave forms a dazzling ice palace.

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

An extensive collection of ancient Egyptian artifacts and mummies.

A volcanic tunnel illuminated by natural skylights offers a shaded respite from the desert sun.

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

Lucha Libre (Mexican Wrestling) themed taco shop.

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.

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

The unbelievably opulent home built for an infamous newspaperman.

San Francisco Bay's ghost town.

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

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

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

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

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

In a city filled with Frank Gehry buildings, one stands out as one of the architect's weirder works.

The largest drain hole in the world.

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.

A faux European lane smack dab in downtown L.A.

The tea room that pushed the boundaries of adorable straight into...we can't find the words.

A ghost town at the airport is now a refuge for blue butterflies.

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

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