Coopers Tower is located near the Dominican monastery in Bistrica, and is the only one of the towers whose curtain wall has been preserved through restoration. It is a rectangular tower, with four floors, and a height of 10.50 meters. They played a role in observation and shooting when it served as a fortification tower, and today the importance of these holes is that they allow sunlight into it, which contributes greatly to obtaining an amazing and unique interior lighting.