The 13^th-century Oświęcim tower is the oldest building on the castle hill. It was built of brick on a square plan with walls about 4 metres thick. In addition to its guarding and active defence functions, the main purpose of the tower that determined its architectural shape was to shelter the inhabitants of the castle at the time of danger. It was supposed to be the last point of defence. The only entrance to the tower was located 10 metres above the courtyard and could be accessed via a ladder or wooden stairs. The high bottom level housing a dungeon prison was only accessible from the upper level that housed utility rooms. The tower was extended in 1512-1513 and the stone portal surviving to this day replaced the porch supported on stone corbels on the southern façade. It was probably also at that time that a clock mentioned in 1549 accounts was placed there. After the Swedish invasion, the tower remained in a state of disrepair for more than 200 years. Karol Kaszny renovated the building at the beginning of the 20^th century. Defects in the tower wall were repaired at that time and the upper level was covered with a tent roof. The tower was connected to the castle in 1928-1931. In 2010, the conservation overhauls was completed and the tower was opened to visitors.