This is the Norman chapel on the clifftop at St.Aldhelm's Head.Archaeologists say there is evidence that where the cross now stands proud on the roof of the chapel,there was once a fire basket,presumably to act as an early warning beacon for Corfe Castle,5 miles to the North.Apparently,the top of the castle could be seen from the roof of the chapel.
The small slit window,is the only window in the chapel.
see http://en.wikipedia.org/wiki/St._Aldhelm's_Chapel,_St._Aldhelm's_Head