I've been having the same problem. I think its just a glitch. I have an idea on how to fix it, but i havent been able to try it yet. Here is my idea. You have a friend save their game on top of the tower next to the alter. Then your buddy needs to load the saved game under multiplayer so both spawn on top of the tower. Im not sure if it works, but im probably gonna try it tonight.

there is a back way in to airedale, but it is hard to get to. there is a small canyon next to talendor you must go through th swamps at the lost lake follow them to the river sw cross the river and then head due south this is the long way but it does work I had the same problem and finally figured aout a back way in you can do a search for a dungeon lords map that is what I did

fletch

Ive been playing the game for a while but all i have left is geting into Arindel. i cant
get to the alter on the top of the tower and ive got no one else to play with. If You guys
find out anything that works plese post it. I will be checking pereodicly.