A Damp Tunnel                                          -      -     NE 
(-------------------------------------------------)     - <---(M)---> -
                                                        SW     -      -

This tunnel extends for as far as you can see.  There is water dripping
from the ceiling, and the walls are covered in a film of water, almost like
dew.  The temperature here is temperate, and very humid.  The tunnel was
made unmistakably cleanly, and the walls are very flat, almost as if some
arcane magic had caused this.  The tunnel ends here, but there is something
strange about the wall to the southwest.