A hole in the south wall, providing a view of the southern walls below.
One of some pictures of what I call the south end building. On the map I later added this is "Tower M".
I do not know more about it. It has a couple of what must have been windows from the start, as well as some large holes in its walls that probably are results of neglect or attack. A staircase leads to its top. One can see there is some substructure that I did not dare enter. Wikipedias has "There are also utility vaults used for storage. " That's what they may be.