A Leafy Underground Glade                              NW     N      - 
(-------------------------------------------------)     W <---(M)---> -
                                                        -      -      -

Although the igneous rock walls of this cavern 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 vegetation here allows a variety of different insects to survive
in the area.