A Spellplagued Land
Toril and Abeir, held together in the natural world, are situated amid other planes of existence.
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.
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 thedimensions to whatever end they desire.