Yep, that is the portion. Just was always curious about that.
Yes, the more I look at that, the more I wonder about it. In the bottom of the bay, there's a dark mass. Could be just a stack of materials, but it also makes me think of machinery. At first I wondered whether this bay could be some kind of lift shaft. There was elevator technology by then, but I don't know whether it had the capacity to be used in a setting like this.
Also, aren't there some wooden panels lifted at an angle on the roof? Made me wonder whether they could cover a hatch opening. Or maybe they are there as fencing or revetment or something...
Anyway, I created a detail of that area: