The only monument of Aci Castello are the remains of a castle built on a rock by the sea in 1076 by the Normans on the foundations of earlier Byzantine fortifications. A settlement developed around the castle, especially after the eruption of Etna in 1169, when the inhabitants of the areas closer to the volcano had to leave it. For some time, the castle belonged to the bishops of Catania, and after the wars fought after the outbreak of "Sicilian Vespers" in 1282 (the uprising of the inhabitants of Sicily against the then ruling island of Anjou) it was in the hands of Ruggiero di Lauria, admiral of the Aragon fleet, who supported the insurgents and then took power; later, depending on the political situation, the castle and its surroundings changed hands many times.
Today, the castle houses the Museo Civico, with a small archaeological and natural collection.