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.  The dampness has pervaded the walls much more here than elsewhere, and
the moss colonies grow rampantly on the walls and floor.