The Castle Wall
Visit to the tourist attraction of Sweden - the part of Visby city wall - The Castle Wall: located in the south-western corner of the wall was originally a tower called the Sail Tower.
Wikipedia: The remaining foundations of the tower show that it was stronger than the other towers along the southern part of the wall. A flanking wall went from the tower down the slope to the sea, prohibiting passage on the outside of the part of the wall facing the sea. Next to the remains of the Sail Tower, parts of that wall and a gate in the earliest wall remain. This gate also served as a passage between the inner courtyard of the Visborg Castle and the outer defensive structures.