The Fortress of Prizren, usually called Kalaja, is the climb that makes sense of the city. From the lanes above the old town, a steep path rises to the stone walls and open plateau where Prizren's medieval stronghold watched the Lumbardhi valley and the trade routes below.
The ruins are atmospheric rather than heavily interpreted, but the view is excellent: minarets, church domes, tiled roofs, the river, and the mountains all line up below you. Go in the cooler part of the day, bring water, and allow time to wander back down through the hillside neighbourhoods instead of treating the fortress as a quick photo stop.