Burg Giebichenstein straddles a rocky bluff over the Saale river at the northern edge of Halle. There are really two castles here: the ruined Oberburg on the cliff above, dating from the 10th century, and the still-inhabited Unterburg below, used today by Halle's art and design university.
The ruins above can be visited freely and give the best view in the city — the Saale curling away, the wooded river bank, the spires of the old town in the distance. The walk up from the centre along the river (about 30 minutes) is itself a highlight. A café in the Unterburg makes a good lunch stop.