You must have killed the king and have his treasure key. On the first level map there should be a small black (uncovered) quadrat approx. in the middle. This is an area you can reach thru a secret door. To find the door go in the adjacent rooms, go very near the walls, it is there somewhere. In the secret rooms are stairs down to another dragon fight. There is a room down there that can be opened with the key, in there is also the note.