Damp Tunnel                                            -      #      - 
(-------------------------------------------------)     - <---(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 to the south
is unobstructed, but there is a large boulder blocking a hole in the wall
that leads north.  You can hear a very loud roaring noise coming from behind
the boulder.