My (namhas) idea of spirit world is like this:

There should be three dimensions or planes:

  Normal world
    - there can be several portals through the line between spirit
      world and normal world, and maybe special astral plane but
      i didn't like the idea that souls of dead mortals come to
      astral plane, imho they need to go spirit world's first plane,
      however spirit world's first plane is like astral plane,
      which is better idea: to do astral plane and spirit world with
      two planes and less use or to do spirit world with three planes
      and more use, i mean more use because it is one full thing

  Spirit world
    - formless dreamlike world with 3 planes

  Godzone or whatever
    - the place where gods' normally are
    - normally mortals can't enter to this plane, but it still
      can be possible

Between normal and spirit world can be special 'reegio' things
or what ever ondoval described in /open/ondoval/something and it
would be one way to enter spirit world. There can be also many
other ways, example shamans can enter to spirit world easily using
special rituals. Spirit world consist of three planes: Outer,
Middle and Inner. Description for there is easy: Outer planes has
weakest spirits and Inner has strong ones. Mortals that are in
spirit world and has too low pow and skills to travel in spirit
world can't move by their own will. They will move by random
table and when they throw certain number they will move to next
plane or backwards. They can't leave spirit world without help of
shamans etc. or divine help.

Whatever.
