If done properly and economically it could be a seperate set that features a pair of defense towers, a short bridge and a tall gatehouse to sit across an imaginary moat to the castle. It could dial upward using a simple Technic axle, gear , gear-teeth lining the edges of a plate-based portculis and the 4-handle endpiece in the current King's Castle Siege for the figures or builder to turn. It is accomplished in one of the new Indy sets coming out. String and pulley designs are also possible, and cheaper still, but less fancy-pants.
And we all know that building castles is all about being fancy-pants.