Finally, I found my way into the tower and the necromancers gave me their quest. Outside the tower I found a key of some sorts and I still have a skull in my bag, but I have no idea how to get into the chambers beyond the huge doors. I find no way to teleport fast the bars, no hidden levers and the necromancers just repeat the same dialogue over and over. I'm completely lost, again.
Any hints, please?