Shallow Lake Waters                                    -      N      - 
(-------------------------------------------------)     W <---(M)---> E
                                                        -      S      -

You are swimming through the waters of an enormous subterranean lake. 
This section is just shallow enough for you to stand on the bottom, but it
is much faster to swim rather than wade along.  The water is dark and murky,
and it is impossible to tell what lies beneath the surface.  You doubt that
anything dangerous could survive this far underground, but you keep your
eyes open just in case.  You can see the shore of the lake to the west.