On my way to the Muir Woods I drove up the Marin County side of the Golden Gate Bridge for a wonderful view of San Francisco. I ended hiking through a cement tunnel in the hillside to the site of an old WWII artillery gun emplacement. This cannon protected the opening to San Francisco harbor against attack.
In the center of the tunnel a corridor appeared that was so dark that you could not see your hand in front of you. Like a curious fool, I slowly walked into the dark room hoping not to fall into a pit or something. I fired off a shop with the camera for lighting and found a gallery of interesting graffiti.
Up on the cliff overlooking the Golden gate Bridge and San Francisco.
Former gun emplacement.
Huge cannon peered out from this protective hat.