I recently went to Harry Potter world, towards the end is a huge model of Hogwarts they used to film the outside shots.
I noticed this tower
It stands a long way (over the other side of the bridge) from the main castle and I can't see a Whomping Willow nearby so I really don't think it's the Shrieking Shack!
Here's a second (slightly blurry) image from another angle
What is this isolated tower?