Tubular Cavern                                         NW     N      - 
(-------------------------------------------------)     W <---(M)---> E
                                                        -      -      -

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.  You
can see a cavern identical to this one through a hole in the wall to the
east.