Okay technically this one isn't a castle. But I think we can assume these LEGO walls are attached to a castle of some sort. Don't you?
This is a rather clever two part design because on the one side, as shown in the first photo you have the invading army attempting to scale the wall, but then when we see the other side (in the second photo) we get to see the defending peasants/militia.
Very nicely done.
Source: Flickr - Brother Steven