Zerith, like all mortal worlds, actually have 3 versions. No version is first, or last. The the destruction of one will be the destruction of all 3.
The Mortal World: this is the version of the world that is the most central of the three. It tends to exist in balance of the other more extreme versions of the world.
The Feywild: This magically infused version of the world is home to the fey. Magic runs thicker here, and the realm is governed by the seasonal Realms.
The Shadowfell: This dark mirror is a place of shadow, fire, and death. Little is known about it.
The diagram below is pulled from a planar manual found in Sigil - the world shown is not Zerith, but the general layout and concept is correct.
