A Perfectly Smooth Corridor                            NW     -      - 
(-------------------------------------------------)     - <---(M)---> -
                                                        SW     -      -

  This corridor doesn't last long, even as long as the last.  It quickly
branches out to the northwest, the same as this corridor from the last, but
at a ninety-degree angle.  Its slope slightly increases, but aside from that
it is no different from the previous circular corridors.  The walls are
constructed, or possibly hewn from, the same black-grey as they were
southward.