Bolton Castle in North Yorkshire

You're standing at Bolton Castle, right in the middle of Wensleydale in the Yorkshire Dales. Take a look at those walls. Tall and stern, aren't they? When Mary, Queen of Scots was held prisoner here, her keeper Sir Francis Knollys wrote that it was the highest walled house he had ever seen. And it had just one way in. The castle forms a square around a central courtyard. That's what's called a quadrangular castle.