There are low hills on which the city lies rise gently from the deep blue waters of the straits. A noteworthy elevation is the 200-foot-high (60-meter) limestone ridge that slopes up from the east and culminates in the heights of La Cabaña and El Morro, the sites of colonial fortifications overlooking the eastern bay. Another notable rise is the hill to the west that is occupied by the University of Havana and the Prince's Castle. Outside the city, higher hills rise on the west and east.