[2] Its main purpose was to protect Sweden's interests in southern Finland against the Hanseatic city of Tallinn.

The layout of the castle resembles a capital 'D', with a round, thick-walled donjon on one corner and the straight part of the D forming the keep, and an inner bailey in center.

The sea level became lower over time due to postglacial rebound, and it became increasingly difficult to approach the castle by boat.

Battles were fought between Swedish and Danish forces and even pirates over control of the castle in the Middle Ages.

The theatre was founded in 1966, and gives numerous performances in Swedish every year in July, often with a connection to the castle history.