On a beautifully clear and sunny day just before Christmas, I went on a walk with Lydia and her mom along the bay at Crissy Field. At the end of the walk, located directly under the bridge is Fort Point, an old US Army fort built during the Civil War to protect San Francisco against Confederate or foreign military attack. (I know, that would have been a way nicer posting during the civil war than say, Antietam.)
Anyway, the fort was open and we were able to walk around inside (it is unsurprisingly spartan) and along the open rooftop where a spread of cannons were once located. The air was cooler on the roof and a bit of breeze was swirling around under the bridge, so we didn't stay too long. But before we left I was able to get a few pictures from directly under the bridge.