Normally, you get back to the rooms where once Fergus resided naturally - at the end of Act I. You can even visit all the cells there.

So I guess that's the reason why it isn't mentioned in walkthroughs.

So I'm not quite sure what exactly you mean ...

When you find a big kettle of crazy, it's best not to stir it.
--Dilbert cartoon

"Interplay.some zombiefied unlife thing going on there" - skavenhorde at RPGWatch