Nice! I initially assumed this shot looks down a spiral staircase, but I suppose it could just as well be looking up at the bottom of such a staircase. In fact, with no handrail in sight (expect maybe in the corner?) and little evidence of wear on the steps, I almost suspect we're looking up. Care to say which it is?
This shot is from Fort Pulaski, in Savannah, Georgia. It is actually looking down. The wall IS the railing. The staircase is in the corner of the fort, leading from the ground level up to the top level where the cannons were. You can see a picture of the fort at http://www.forttours.com/pages/fortpulaski.asp.