In the northwest corner of the defensive walls stands a corner tower, built on a square plan, hence called the Square Tower, with a side similar to the longer walls of the Ivy Tower base (about 11 meters). It used to have two pointed arch gates facing the city, but they are now walled up. On the other side, facing the moat, there are three rectangular, arched shooting galleries, with cheeks spread inwards. Due to the lack of iconographic sources, it is impossible to reconstruct the original top of the tower. During the adaptation into the headquarters of the Main Technical Organization branch, a third well-preserved floor was added to the two existing ones, and the whole was closed with a tent roof. St. James's Church in Lębork.