So many of our favorites have already been mentioned, but another GREAT one to do at night (even if you'd never consider doing it during the day) is Swiss Family Robinson Treehouse. Aside from the special feeling of being in there when it's dark, there is a certain landing point at which you get an utterly spectacular view of the castle all lit up; during the day, you don't even notice this viewpoint. If you're a photographer, you may want to make a point of seeking this out.