Torre di Sulis is the tallest and most substantial of Alghero's surviving towers — a 23-metre cylindrical structure built in the 14th century at the south corner of the city walls. It served first as a defensive bastion, later as a prison, and is now a small exhibition space hosting rotating contemporary art shows on three floors connected by a stone spiral staircase.
The roof terrace, accessed at the top of the climb, gives one of the best panoramic views of the old town. The walls converge here at the southernmost point of the historic centre, where the medieval city meets the sea. Open most days April through October; off-season opening is irregular.