City of Splendors & Horrors
Most theoreticians place the Astral Sea, domain of the gods and resting place of their dominions, above the world. A mixture of energy and elements exists below in the Elemental Chaos; at its bottom, the Abyss roils with demonic malice. Alongside the world are its reflections: the mystical Feywild, a place of boisterous life and magic, and the gloomy Shadowfell, a dim realm of decay and apathy.
The Spellplague began, for all intents and purposes, in the dominions of the gods. Cyric murdered Mystra, unraveling magic in the cosmos and destroying her dominion. At the same time, Abeir and Toril happened into alignment. This cataclysmic coincidence led to upheaval, shaking apart the primeval order, opening up holes in defenses, and reshaping elements. When it was over, a realignment of power had brought forth a new order—the cosmos as it exists today.
In many ways, the planes are easier to explore than they were before. Although many otherworldly locales are hostile and no place for any sensible mortal, few places have features that kill a visitor outright. Those who have the power can travel the dimensions to whatever end they desire.