Could we have them doors extruded juuust a little bit from the outside model? A character basically can't enter unless he moves at between 75 and 105 degrees angle to the door surface. And - and! - we can't enter the main door riding a horse! So much for my Caligula and Incitatus cosplay =(
In all seriousness, though. There is no reason for those (multiple, yay) doors to be less accessible than a simple door of a simple wooden house.