OK, I just re-watched my video of the Travel Channel Disney episodes and they do mention the apartment in Cinderella's Castle, but they do not show it. They say that it was used by telephone operators in the MK years ago, but has remained empty since the switchboards were moved. I wouldn't be surprised if there were many hidden areas scattered around the parks, but doubt that just anyone can wander at will whereever they want. Can you imagine the legal/insurance problems this would create?!