Main Furnace                                           -      #      - 
(-------------------------------------------------)     - <---(M)---> -
                                                        -      -      -

This cramped chamber is full of flames and smoke.  It burns from an
underground autonomous source, and powers the bellows which the smithies use
around the place.  Small pipe holes are in the ceiling to allow heat and
smoke to travel around the area.  The ground is literally on fire and the
place is steaming with smoke.