It can be a challenge to find a unique perspective on capturing some of the things that make a good castle work on a small scale. But I think this model by Dwalin Forkbeard really nails it. To begin with, the multi-angled rockwork and landscape is an excellent rendition of techniques more commonly seen on a much larger scale.
Using loosely connected plates curved into an arched bridge is genius, and the wooden window shutter makes the perfect gate door. The fact that each tower is a different size and the combination of stone and wood create a neat effect as well. And did you notice the minifigure helmet as a roof of that interior tower?