A Tunnel Sloping Downwards                             -      N      - 
(-------------------------------------------------)     W <---(M)---> -
                                                        -      -      -

You are walking along a tunnel, that slopes downward to the north.  The
walls are cut from the dirt, and as you touch one side, a small piece of
dirt falls down.  The ceiling is relatively low, and the ground very hard. 
To the west you can see light, and is the enterance to the tunnel, and north
the tunnel gets darker and darker.