I've been wanding around and stumbled across a sewer entrance. It's full of Assassin Lizards, ghouls, corpses, zombies and giant spiders. I've cleared it out and have been wandering around for hours looking for the exit. I've only found a single level to this sewer from what I can tell.

I thought I found the exit at one point - a stairway at the extreme north of the screen but when I enter some big bald guy kills me within 2 hits. Is there a way out of this sewer or am I just SoL?

Check your auto map to find the way back to the exit, east of where you are. From the spot you are now (the executioner in the jail) if you head slightly south, east and north, there is a shortcut to get you just west of the exit.

Yes just to add,there is only one level to the sewer.

When you exit you should be in the middle of the market town in Ars magicani(sp?).

this is why you should make notes on the map of where the exits are. <img src="/ubbthreads/images/graemlins/mage.gif" alt="" />

one more things to add.
in that sewer, there's would be a passage to go to another sewer
of the merridell (a town on the north and a bit east) too.