Concrete strongholds stand guard over the Golden Gate.

An abandoned, unfinished mansion on grounds strewn with lava rocks.

Across Ring Mountain is a vast collection of Native American petroglyphs unique to the region.

The Flatiron Building's storied West Coast cousin is a lot more into religion.

A restored 1920s cascade stairway provides one of the best views of Oakland's Lake Merritt.

Julia Morgan's Moorish-Gothic labyrinth of fountains, trees, natural light and Oakland's notable dead.

A B&B on a Victorian lighthouse station in San Francisco Bay.

Abandoned landscape once home to "the world's largest winery."

Once the largest winery in the world, this castle-like building now sits abandoned on the San Pablo/San Francisco Bay shore.

At 16,627 feet above sea level, this unstaffed station is the highest in the world.

Nuclear waste dump site now an environmental sanctuary.

The graffiti-covered remnants of a former triangulation station are balanced precariously on this California peak.

The sole surviving relic of the San Francisco neighborhood cobbled together from old horsecars and streetcars.

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

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

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

A modest reminder of treacherous waters at the Golden Gate.

9,000 square feet of vintage and modern mechanical toys, dioramas & sideshow curiosities.

A sparse, solitary sequoia still stands as a living tribute to the famous conservationist who planted it—but it's dying.

This mountaintop beacon is only lit three times a year but shines like some kind of all-seeing eye.

Haunting and beautiful trees, doomed to die.

Where a staggering 747 ships were constructed during World War II.

Once America’s most beautiful army base, this abandoned military fort on the coast of Monterey Bay has been left to the elements.

This municipal playground was co-created by the father of one of the most playful characters ever.