A Poorly-Hidden Passage                                -      N      - 
(-------------------------------------------------)     - <---(M)---> -
                                                        -      S      -

This passage looks as though it was intended to be unseen by anyone who
didn't know of existence, but it has obviously failed horribly.  The
doorway, not even placed in the shadows, is broad, with a clear view from
everywhere in the frosty, bleak house.