Those Engineers, always building stuff, even when there's something already there.
Fort Morgan's the one on the left. Battery Duportail is that big block of concrete to the right. Before 1898, Fort Morgan had a big, open parade ground with impressive granite stairs at each of its five corners.
Military guys being the way they are, they wanted some big 12" guns parked right in the middle of the fort. Guns need a bunker, and before long there was this honking big mass of concrete poured right over a few parts of the old fort.
Most of the fort is accessible. For this spot, you have to walk halfway around the outside to the fort's "back door" in the southwest face of the south bastion. This will let you see a little Boy Scout barracks, part of the latrine of the old citadel, and at the opposite end these stairs. You'll have access to most of Wall #3 and all of #4--and a generous length of gray concrete.
At the bottom of the page on that first link, there's a little Google Map window that'll let you get a good view of things; this corner's all the way to the left in the wedge formed by the fort's and battery's south walls. The latrine foundation is a neat square near the fat end of the triangle.