The quarry tower, where they blew up the mine entrance, can be done later. The tops of the walls and the tower itself will be above the poison gas. There are two black ring guards on the first floor (which I took out at level 16 or 17 with help from my creature), and people upstairs that you eventually need to rescue.
The top of Lovis' tower will be accessible after getting the battle tower, though the door to his chamber will be locked. Dr Needleman's storage area is above the poison gas (Bellegar can teleport you high above there (so you fall down to it) before you have the battle tower, but you can not get in until you find Needleman later, without his mindread-blocking helmet (though there is nothing of any great value there).
