if i remember right, the crystal is in the top most part of the tower...go up as far as you can via ladders and you will find a few statues that you have to turn into the correct positions to open a gate ...carry on up and you come to a door which you can enter...inside you will see 4/5 small alcoves one of which has a skeleton tradesman in....the crystal i think is located when you pull on 3 or 4 chains inbeded in the walls around the room
