Each and every casemate along Fort Pike's walls is connected to the parade ground by a tunnel such as this one...which was unusual for the later starforts of the United States, whose casemates were connected to one another. It made sense to isolate each firing position, since one exploding gun could easily take out the crews in its surrounding casemates if connected, but assumedly this was decided to be less of a danger than the inability to communicate with surrounding guncrews. I hope you like this tunnel, because you'll be seeing a whole lot more of them!