0m       1km       2km       3km       4km       5km       6km
      |---------|---------|---------|---------|---------|---------|
      ===================================================================>
      <===================================================================
      |---------|---------|---------|---------|---------|---------|

                         you are not here
                                |
                                v
                         [ maintenance ]

  A circle is a corridor which has learned how to keep a secret.
  Walk far enough and every exit becomes the entrance.

  stairs                                              continue clockwise