Many moons ago I lived on the Presidio of San Francisco as a teenager. It used to be an army base, and at the time it was transitioning to a National Park, but military personnel still lived on it. By the way if you want to live in the house that I did, it's yours for the low low price of $7500 a month in rent, plus utilities, car permit, pet fee, etc. Rare is the city that is more costly to live in than Fairfax, but San Francisco manages to pull it off.
Anywho, the Presidio(and Marin Headlands) is riddled with shore defense batteries. The best preserved is Battery Chamberlain along Baker Beach. Farther South you have Battery Davis which once housed a 16in Casemate gun(extremely similar to the main battery of late model USN battleships).
Ten will get you twenty most folks in San Francisco have never visited these sites. If I go back, I'll probably take pictures.
Anywho, I saw this video of a Taiwanese shore defense gun, which made me think of my time living on the Presidio.