Yeah, the sewers are the ones in the copper coronet, not the ones under the temple district.

Does anyone know how to find the Hidden, in Jan's quest to save the little girl's life? I've spent hours waiting around in the sewers!!

The Hidden is in the same hallway as where you killed the kobolds, the part where there is a petrification trap on the bridge. Just walk as far west as you can, keep to the northern side of the water. Hmmm... it's a bit hard to explain but I hope you'll find him. Btw. if you spent hours walking around, be careful that you do not exceed the time limit on this quest because then Jaella will die