A Tiny Islet                                           -      N      - 
(-------------------------------------------------)     W <---(M)---> E
                                                        -      S      -

You are standing atop a small pile of rocks in the corner of a massive
subterranean cavern of some sort, surrounded by a huge underground lake.  It
is impossible to see the other edge of the water through the darkness, but
you can swim to the west or the south if you want to try and find the shore.