Grimrock

Oh crap, really? Now I feel dumb. Thanks, you are a lifesaver!

Near the start of the level, where there is a sign that says shelter left, cells right, I go through a short hallway of three cells. At the end is a key door, but I can't find the key anywhere. I also see no buttons, no teleporter that other forums posts have mentioned. Nothing. I know I've got to b...