Borj Sud is the southern counterpart to Borj Nord, a 16th-century hill fort built to watch over Fez. The fort itself is usually secondary to the view: from the slopes around it, the medina spreads below in a dense, pale maze, with minarets, ramparts, and the surrounding hills finally making sense.
Come in the late afternoon if the air is clear. The walk up is possible but exposed, and a petit taxi saves energy if you have already spent hours inside the medina. It is a good place to reset your mental map of Fez after getting lost in the lanes.