The Obertorturm (Upper Gate Tower) dates back to the 13th century. The inside contained a prison and the tower keeper’s residence. The geared clock from 1532 can be admired on the 9th floor to this day, and in the attic there is a carillon (“Glockenspiel”). The Upper Tower is open to the public. Information on guided tours is available from the tourist office "Aarau Info".