Fort Point

We've known for a long time that there's an old fort directly underneath the southernmost part of the Golden Gate Bridge.  Finally, after 20 years, we decided to visit it.

It turned out to be a large, interesting structure -- built in the 1850's, all brick, and very well preserved.  It defended San Francisco Bay from the Confederacy during the Civil War, served as the headquarters for building the Golden Gate Bridge in the 1930's, looked out for Japanese submarines during WW II, and finally became part of the National Park Service in 1970.

It's full of interesting archways and corridors.

Probably the best part is that because it's directly underneath the bridge, you get amazing views of the Golden Gate Bridge's structure.