A Lush Cavern                                          NW     N      - 
(-------------------------------------------------)     W <---(M)---> -
                                                        -      -      -

The caves in this section of the mountain are completely unlike anything
you've seen before.  Although the igneous rock walls make it quite obvious
that the chamber was formed by volcanic activity, the floor is covered with
a thin layer of soil and there are a variety of plants growing everywhere. 
The temperature here is much higher than in other areas you've passed
through, and you wonder if the lack of sunlight has caused the plants to
develop the ability to transform heat energy into food.  Whatever the case
may be, the unique ecosystem allows some creatures to survive here while
they have become extinct everywhere else in the world.