A 140-year-old castle with underground caves hidden in San Francisco.

A huge musical instrument played by the ocean.

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

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

A strange house built only at night, with rumored mystic inspiration.

Another of California's unused Cold War missile defense complexes has become a graffiti gallery.

An ominous concrete cube cuts a dystopian silhouette atop this California mountain.

Before it was abandoned and left to rust alongside the road, this riverboat starred in a John Wayne movie.

The remains of a deserted steamboat sit rusting beside an old ferry pier and an abandoned train platform.

An abandoned car and strange wooden debris are among the scattered remains of the old sand and gravel quarry.

An abandoned Cold War missile radar site.