A fifteen-minute walk south along the coast from Acitrezza brings you to the Norman castle of Aci Castello, a striking black basalt fortress perched on a lava promontory above the sea. The castle was built in the eleventh century on top of an older Byzantine fortification, and its position — essentially a plug of ancient lava jutting into the water — gives it a dramatic, slightly improbable look.
Inside, a small archaeological museum holds finds from the area including Greek and Roman ceramics, amphoras recovered from the seabed, and medieval objects found in the castle itself. The views from the battlements up and down the coast are excellent, and on a clear day you can see Etna with its permanent plume of steam or smoke.