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

You are walking through a small tunnel that leads deeper into Hellbent
Mountain.  Unlike the passage you traveled through earlier, the walls here
are rough and rocky, and look like they formed over a long period of time. 
Clearly, the caves were created by erosion and not volcanic activity, and
you feel slightly silly at having entertained such a ridiculous idea in the
first place.