The impressive castle dominates Bosa from above. It was built in 1112 on top of the hill of Serravalle by the noble Tuscan Malaspina dello Spino Secco family, who settled on the Island in the middle of the 11th century. It is said that the jealous marquis built an underpass from the castle to the cathedral so that his beautiful wife would go to church without being seen by indiscreet eyes. One day, in the throes of an attack of jealousy, he cut off her fingers and wrapped them in a handkerchief, that he took out of his pocket, forgetting his madness, in front of his friends. The fingers fell out, uncovering his crime, and he was imprisoned. Legend also has it that several of the rocks of the castle are the petrified fingers or the witnesses petrified by their horror.