The celebrated eyesore created by starry-eyed sweethearts.

From the Difference Engine to the Cray-1, all under one roof.

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

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

Inside an old airplane hangar, friends and strangers alike play on a massive trampoline.

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

An elaborate gift from Claus Spreckels is now a piece of San Francisco history.

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

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.

These subterranean storage areas hold emergency water reserves.

Art from the latest counter-culture; kids who dye their hair blue and believe the future will be a post-apocalyptic water world.

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.

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

Furniture tries to escape an abandoned building in San Francisco.

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

San Francisco's oldest surviving monument and meeting place for 1906 survivors.

Only hotel where you can legally launder money.

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

Longest road tunnel in the world features an air treatment plant and the illusion of daylight.