That’s the formal chancel at the end, although I’m not sure whether this was a monastery solely for the monks or whether local parishioners were able to use it. At the crossing, so not far in front of where this photo was taken, were the graves of Kings Sverker I, Carl I, Sverker II and John I. The graves weren’t swept away after the Swedish reformation as they were found when the abbey was cleared by an archaeologist in 1827.
And the nave. If the Reformation hadn’t of taken place, or if this church would have continued in use, the link with the former Kings of Sweden that were buried here would have likely given it some considerable status.
I have no idea how so much of that roof has survived over the centuries….. Decent builders is all I can think.