Malaspina Castle dominates the town of Bosa from the hill of Serravalle. He is isolated from the city but the tradition goes that is connected to the cathedral and the church of St. Peter's galleries and underground passages. There are numerous legends associated with it: love stories, passions, jealousies and sorrows that make it emblematic for the city of fear. Was built from the early decades of the twelfth century (the date determined by Fara but contested and recently moved to the thirteenth century.) By the Marquis Malaspina, originating in the Lunigiana.

It is accessed through S'iscala 'and knows pink, a long staircase placed laterally to the district of Sa Costa, or even by car, take the road for a stretch along the cemetery.

Its construction would be an effective defense against attacks by Arabs who were easy access through the mouth of the fear that originally were two.

With its construction the residents of Manna Bosa, located near the church of San Pietro, moved across the river, building their homes at the foot of the castle for protection, giving rise to late-medieval district of Sa coast.

The castle has undergone over the centuries, numerous changes: four towers were added in 1185, while in 1300 it was enlarged the walls. Also in this period was the construction of the tower by teacher probably Sardinian architect John Capula built trachyte ocher and a basic trachyte.