Tubular Cavern                                         -      -      - 
(-------------------------------------------------)     W <---(M)---> E
                                                        -      S     SE

This strange cavern is about fifteen feet wide, but it is also almost
completely round.  Luckily, the bottom is somewhat flat, allowing you to
walk along without stumbling.  You wonder how a nearly perfect tube like
this could have formed naturally, and begin to suspect that the Dark Power's
influence extends even this deep below the entrance to the mountain.  There
is something strange about the west wall here, and when you stare at it you
begin to notice that it shimmers and wavers before your eyes as if it were
not quite solid.