A Round Tunnel                                         -      N      - 
(-------------------------------------------------)     - <---(M)---> -
                                                        -      S      -

You are walking through a small tunnel that leads deeper into Hellbent
Mountain.  The corridor curves gently to both sides, and you imagine that
you could follow it all the way around in a circle and end up back here
again.  The outer walls are made of a smooth black rock, but the interior
walls seem to glow with a dim red light.  Upon closer examination, you
realize that they are in fact red-hot, and seem to be slightly viscous. 
Could it be that the mountain is actually a volcano?