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.

Not merely a museum – but a whirring powerhouse that offers a subterranean peek into the heart and soul of cable car operations.

This turn of the century masterpiece has a mysterious goaty interloper.

An overlooked and unassuming engineering marvel.

A collection of memorabilia from the Beat era in the back of a San Francisco bookstore.

This private residence was the template for one of the most beloved television homes of all time.

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

A still functioning vaudeville carousel that has operated for over a century boasts a colorful menagerie and past.

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

A hidden subterranean installation offers a view of the sky.

The remains of a ruined mansion memorialize the 1906 earthquake.

The oldest burial ground in the city, final resting place of city founders, Ohlone natives and murderers alike.

Nestled in the heart of San Francisco’s bustling Financial District stands a unique homage to the Mayan and Beaux Arts.

The last remaining relic of San Francisco's glittering 1915 Panama Pacific Exposition.

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

An essential stop before plundering, BYO Cutlass.

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

A shop full of natural curiosities, carnivorous plants, and costumed taxidermied mice.

Tiki luxury on Nob Hill.

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

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

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

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