Humid 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.  The tunnel is unobstructed to the south, but to the north there is
a large pile of stones blocking your way.  Perhaps with a bit of effort it
would be possible to move them out of the way.