The idea of a large castle is a good idea, perhaps every room could show something from a different fairytale? The castle shouldnt take up all the space though, there could still be room outside for other scenes.
Here are a few suggestions for inside the castle:
-Sleeping beauty room. The room could have plenty of roses in there, maybe some vines if possible, with sleeping beauty laying on the bed and a prince clicky leaning over her to kiss her.
-Knights of the round table room.
King Arthur could stand at the round table and appear to be talking, with the knights sitting around the table. Maybe Merlin could stand in a corner and watch them.
All knights should look friendly though, no dark knights here.
-Cinderella.
At a stairway, Cinderella could be seen walking off with a prince standing on the stairs holding a glass shoe. (might require a little custom work.)
-Gingerbread man.
Using clay, a small gingerbread man could be running amok in the kitchen, with surprised kitchen staff watching him.