three-day tour of San Francisco was, of course, Fort Point. It's the only such fort on the US Pacific coast.
It's open for tours Friday through Sunday and I was there on...a Monday.
Reminds me of that time I went all the way to Fort Pike on a Saturday to find it closed and fenced-in.
Since Fort Point is a National Park site, there's a clearly-marked schedule, something the Louisiana parks people didn't think of ("What? A schedule on a sign? Why'd anyone need that? We know when we're open!"). Oh, and Fort Point is open ON WEEKENDS, which makes sense for attracting tourists, something else the Louisiana people didn't consider ("What? Make the fort open on weekends? But that's mah fishin' time!").
At least this one's only half-fenced off (basically the northern and western fronts), probably as protection for the Golden Gate bridge, which runs directly overhead. The bridge's chief engineer Joseph Strauss saw something worth preserving in the fort, so he designed an arch to carry the bridge over (link goes to a tour site; very good picture of the arch).