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.

Golden Gate Park's historic collection of plants.

The remains of a ruined mansion memorialize the 1906 earthquake.

In this century-old literary safehouse, print is alive and well.

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

Big gun installations, built over a massive cemetery, now abandoned & hidden in trees.

A nondescript building that's been functioning as a speakeasy for nearly a century and a half.

The randomness of this wall of lava lamps helps encrypt up to 10 percent of the internet.

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.

Staircase winds down the side of Telegraph Hill through gardens, wild parrots flying overhead.

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.

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

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

A favorite haunt of dinosaur loving children and hallucinogen loving hippies alike.

Olfactory delights in San Francisco's Botanical Gardens.

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

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

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

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

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

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

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