The one-time watch house for incoming ships at the Golden Gate now stands abandoned and hidden in trees.

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

A pair of slides and a tree-lined stair corridor have been an urban oasis for nearly 40 years.

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

A tiny theater hidden in an alley plays a constant stream of short silent films for anyone willing to peer through the peephole.

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

Relics of the 1894 Midwinter Exposition continue to delight visitors today.

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

Get lost in this haunting fairytale art walk through a man-made eucalyptus grove.

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

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

A psychedelic labyrinth on the San Francisco bay.

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

A huge musical instrument played by the ocean.