Tour the castle by sourbugger
Unlike the Cathedral that is built on Bedrock, the castle may well have existed for over 900 years, but its had to fight for its survival for all of that time.It could well have ended up as a large pile of rubble in the river at several points in its chequered history.
The Castle became (and still is) a college of the University of Durham in the early 19th Century. This means that tourism has to work around academic activities. It also however means that the Castle has an unending supply of bright engaging students who act as tour guides to help supplement their income.
I know they are all well trained, and many are quite knowledgable.
Tours run every day from Easter to September
and Mon,Wed, Sat & Sun afternoons- although it is worth checking at the porter lodge to confirm that a tour is going ahead on a certain day. It is good value at 3.50 an adult.