--

[IIRC, this spiral staircase picture started out as a diddle of a picture
by somebody else]

       ________                 _________
      |        |               |         |
      |        |               |         |
      |--------|               |---------|
      |--------|               |---------|
 _____|______ @|_______________|________@|_____
||----|---||---|---||---||---|||---||----|----||
||    |---||---|   ||   ||   |||---||----|    ||
||____|___||___|___||___||___|||___||____|____||
                        |_________|
                        |________|
                        |_______|
                        |_____|
                        |___|
                     __|||
                   _|___|
                 _|_____|
                |_______|
               |________|
              |_________|
              |_________|
              |_________|
               |________|
                |_______|
                  |_____|
                    |___|
                       |_|__
                        |___|_
                        |_____|_
                        |_______|
                        |________|
________________________|_________|____________________