This is what remains of the Manuel Nunnery, believed to be the northern portion of the West gable of the curch - everything else has been washed away by the River Avon, that you can just see in the picture.
The nunnery appears to have been built in the twlefth century, and belonging to an order of Cistercian nuns. It was never a wealthy nunnery, and was disbanded soon after the reformation of 1560. It appears that in the 1150s there was one prioress and four nuns resident in the nunnery.
Interestingly, there was an earlier attempt to close the nunnery in 1506 because the nuns were a accused of "living a life alien to the Cistercian rules". I'm going to leave you to choose what that might mean...
Now, it stands at the edge of a field. No marking, no Historic Scotland plaques, nothing. Just a wall in a field.