While in the Bay Area for the DSL meetup, I finally managed to get inside a Third System Fort, specifically Fort Point, built in the 1850s to guard San Francisco Bay. It's a late addition to the Third System, and shows all of the various features developed during that system's life. And if the thought of mid-19th century coastal defenses isn't enough to excite you, you should consider going anyway, because it's right under the Golden Gate Bridge and the area is stunning.

The Golden Gate, the stretch of water between the Pacific and San Francisco Bay, is an obvious chokepoint for anyone trying to protect San Francisco, so the first fortification in the area was built by the Spanish in 1794, with only a handful of cannons. It fell into ruin after Mexico gained independence, but when gold was discovered in California in 1849, only a year after the US seized the territory from Mexico, there was interest in protecting the rapidly-growing city from attack. The result was the only Third System fort on the West Coast, started in 1850 and completed in 1860. Like most of the Third System, it was built with casemated guns inside the walls, although it is unusual in having three tiers of casemates instead of just one, as well as a barbette tier on top of the wall. Unfortunately, just after it was completed, the performance of several other brick forts in the Civil War, most notably Fort Pulaski, showed that rifled guns had made masonry forts like this obsolete, and the fort was placed in reserve, even as new batteries were built starting in the 1890s.
In the 1920s, plans were drawn up for a new bridge across the Golden Gate, and the obvious route went right across Fort Point. The initial plan was to demolish it, but the chief engineer decided to redesign a bit of the bridge to preserve "a fine example of the mason's art". It was transferred to the National Park Service along with most of the old coastal defense areas in the 70s, and opened to the public.

The inside, with casemates
But all of that is just history, and still leaves the question of what it is like to actually visit the fort. Getting there is sort of a pain, requiring as it does a drive through San Francisco, but the actual area is lovely, with views of downtown, the Golden Gate and the bridge. It was a bit chilly and extremely windy, but almost worth going for the views alone. The fort itself is pretty open and very cool to wander around it. There are somewhat minimalist museum exhibits along the south wall, the only one that didn't have cannons in it. On the bottom floor, it's a fairly new overview history of the fort, although it's reasonably low-density, probably because they seem to get a lot of school groups. There are a couple of casemates with vague reconstructions of guns, although less effort had been put in than I would have liked. There's also a collection of old cannons and stuff on that level. Signage is adequate, but not great.

The upper level, showing me, the view, and barbettes
The upper levels seem largely due for a refresh, but it's easier to see the mechanics of the fortification, down to the iron reinforcing plates around the gunports, and there's nice slice-of-life signage and exhibits in some of the areas on the south wall where the garrison used to live. And the top level has incredible views, but is also incredibly windy. My main complaint about it is that there's been no real attempt to install a replica of the mounts used there.
On the whole, I enjoyed my visit, but I'm not sure it ranked highly enough to recommend traveling to see it, or even to put it high on your list if you're visiting the area, unless you happen to be a connoisseur of coastal defenses. But if you're a local, it's well worth taking a few hours to go see, particularly if you happen to be in the area anyway. Or you could do what we did and combine it with a trip across to the Marin side for a day of Defending San Franciso.
Comments
I am now officially jealous - Fort Point is someplace I've always wanted to see. Well done!
There's a reasonable amount of stuff to see in the Bay. I have a couple other reviews coming from that trip, plus stuff from three years ago. Just check to make sure Hornet isn't hosting a furry convention before scheduling.
I visited it in 1999, with a Ranger that explained how to load a Napoleon.
It seems it has not changed much.
I went there recently after not having been for many years. The photos don't show the views out to the ocean or back to Alcatraz and downtown, but it's such a lovely location that even there are non fort-nerds among your party they will have plenty to enjoy. Do bring a wind shell, though, even on a sunny day.