Built as a standard motte-and-bailey fort in 1072, Durham Castle was the prince bishops' home until 1837, when it became the University of Durham's first college. It remains a university hall today. Highlights of the 50-minute tour include the 17th-century Black Staircase and the beautifully preserved Norman chapel (1080). Book ahead by phone, or at the Palace Green Library or the World Heritage Site Visitor Centre; tours run most days, with additional tours during university holidays.
Each successive prince bishop sought to put his particular imprint on the place, but heavy restoration and reconstruction were necessary in any case as the castle is built of soft stone on soft ground.