Massive prehistoric mammals used these stones as oversized scratching posts.

This mountaintop beacon is only lit three times a year but shines like some kind of all-seeing eye.

Hand-powered race of alternative forms of transportation.

This (occupied) house is 10 feet wide and full of spite.

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

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

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

The miraculous hydrant that saved the Mission District in 1906.

Art in the form of a winding, man made crack in stone.

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

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

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

Dive bar built out of the remains of a whaling ship.

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

A speck of nature and art in one of San Francisco’s most notorious neighborhoods.

A mysterious painting of the self-declared Emperor of the United States watches over a local hof-brau.

Early prototype for Frank Lloyd Wright's Guggenheim.

Its buzzing collection honors vibrator history.

The first AIDS memorial chapel in San Francisco and one of only a few in the U.S.

Faceless white figures loom over the city from the rooftop.

There is no trying to fall in love with this Star Wars fountain, you just do or do not.

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

One of the last remaining Carpenter Gothic churches is situated on a wildflower conservatory overlooking the bay.

A creepy steel gremlin has protected the Bay Bridge since 1989.