Richmond Castle was begun in 1071 by Alan Rufus, a Breton kinsman of William the Conqueror, and is one of the oldest Norman stone castles in England. Its huge rectangular keep — built around 1170 and still close to its original height of thirty metres — stands on a cliff above a bend in the Swale and dominates the town from every angle.
The interior is now a ruin, but the keep is intact and you can climb to the top for a sweeping view of Swaledale. Look out for the Cockpit, a small medieval garden inside the walls, and the cell block where conscientious objectors were imprisoned in 1916 — their pencil graffiti survives on the walls and forms one of the most affecting parts of the visit. Run by English Heritage.