Dimly-Lit Corridor                                     -      N      - 
(-------------------------------------------------)     - <---(M)---> -
                                                        -      #      -

This hallway is made out of rough-hewn solid stone blocks.  The blocks
are a dull gray and sort of dusty.  A pale green moss has started to grow in
the cracks between the blocks.  Torches are set in small alcoves along the
walls at regular intervals, but are not sufficient to fully light the
corridor.  The flickering of the torches throws eerie shadows on the walls. 
Is that a trick of the light, or is someone following you?  A porticullis
bars your exit south.