A Dark Tunnel                                          -      N      - 
(-------------------------------------------------)     W <---(M)---> -
                                                        -      -      -

This narrow corridor runs in between two large chambers, and it is so
small that you can barely fit through.  You are unable to turn round or even
look behind you, and you becoming increasingly sure that the strange noises
that meet your ears are the sound of something creeping along after you.