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

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

San Francisco's newly reopened hands-on science museum.

Carnivorous plants, medieval aphrodisiacs, and the largest original wood structure glass conservatory in the western hemisphere.

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

A winding path built in secret on the edge of the continent.

A collection of 20th-century automata, penny arcade games, and musical contraptions.

A museum befitting the city responsible for supplying the majority of the world's LSD.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

The only theatre in the world constructed specifically for sound movement.

Bring your own cardboard to the slippery slopes of concrete hidden in a neighborhood park.

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

A huge musical instrument played by the ocean.

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

A "gravitational anomaly" located in the redwood forests just outside of Santa Cruz, California.

Subterranean house made out of a grain silo, located in the Santa Cruz Mountains.

A pair of pure white felines guard the entrance to a spot of California real estate established as an artist's haven.

The largest permanent Monopoly board makes one of the longest games even bigger.

An extensive collection of ancient Egyptian artifacts and mummies.

The headquarters of a secretive order is also a beautifully-designed park.

A peculiar mansion built by the troubled heir to the Winchester Rifle Company fortune.