A Slick Branch of Tunnel Filled With Noxious Vapors    -      N      - 
(-------------------------------------------------)     - <---(M)---> -
                                                        -      S      -

You are walking down a reeking tunnel.  The smell fills your nostrils and
blinds you as you walk.  The stifling silence is broken once in a while by a
small noise in the area.  The cold and slick walls chill you to the bone as
on.