Castello Ursino is a thirteenth-century fortress built for Frederick II, once standing on a promontory by the sea until Etnas 1669 lava flow surrounded it with rock and moved the coastline. Today it houses the Museo Civico, with archaeological finds and art collections. Ticketed admission allows visitors to explore the medieval halls and museum displays within the imposing dark-stone castle, a striking survivor of Catanias turbulent history.