Concrete strongholds stand guard over the Golden Gate.

Ride on a fully-restored Nike nuclear-tipped missile elevator from the Cold War.

Internationally-recognized arts center housed in a century-old former military barracks.

This lighthouse has been guiding shipping into the Golden Gate since before the American Civil War.

Centuries of biking history are nestled in the shadow of the birthplace of contemporary mountain biking.

George Lucas donated this park to honor the birthplace of his two biggest movie franchises.

Frank Lloyd Wright died a year before construction on his largest public project even began.

The miraculous hydrant that saved the Mission District in 1906.

This one-block alleyway is stuffed with street art that is colorful, cultural, and intensely political.

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

Since 1973, this block has been home to the most concentrated collection of murals in San Francisco.

This colorful boulder serves as a canvas for political statements and artistic expression.

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

Overflowing with shipping containers, this location has been transformed into a massive workspace for artists.

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

Radioactivity still cause for concern at this urban explorer's paradise.

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

Where a demonstration led to equal rights for one of California's most marginalized communities.

A historic office and commercial building located in the heart of downtown San Francisco.

This contorting sculpture is the tallest in San Francisco.

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

Beneath the southern end of the Golden Gate Bridge is the “Gibraltar of the West Coast,” a fort built to protect the San Francisco Bay from naval attack.

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

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