Damp Tunnel                                            -      N      - 
(-------------------------------------------------)     - <---(M)---> -
                                                        -      S      -

This tunnel is quite small, and you are forced to stoop down in order to
walk through it.  The air is heavy with moisture, making it rather hard to
breathe.  You also notice the thin trickles of water running across the
floor make it difficult to walk without slipping.  The tunnel continues on
to the south, and to the north you can hear a low roaring noise.