In Sundering Shadows, the most basic planar mechanics is an unknown enigma. Little can be assumed to be known with certainty. Central to the observable existence is the prime material plane, wherein the realms of Shadow and the other nearby continents lie. Overlapping with this are the Ethereal, Shadow, and Feywild, and bordering it lies the astral. From there, the inner and then outer planes are accessed by way of the astral plane. What lies beyond is subject of forgotten knowledge.
These are the four elemental planes – air, earth, fire and water – accessible from the prime via the astral plane. A few tangible cross-points exist on the material (eg/ the plane of fire has a permanently tethered astral crossing point in the ruins of old Antioch, placed by the maddened wizard Ignatius). Beyond this, powerful magic must be used to reach these planes.
Many outer planes exist, although scholars still debate to this day as to their exact number and nature. Such planes are the realms of Gods and demons, celestials and devils, and the many splendors and horrors that lie between. Certainly reason would suggest that planes such as these must exist to encompass all deities, alignments and natures in some form. Amongst these also lies The Deathless Plane, where the souls of the dead are drawn through the astral plane to await Lysara’s judgement.
Demi-planes are usually only small, and are physically created by a deity or powerful group of spellweavers. Countless exist, mostly only as tiny pockets (rope trick, bags of holding). Scholars also argue that larger, artificially made demi-planes could exist, but usually only powerful spellweavers can create demiplanes.