the Elemental Plane
The Elemental Plane is believed to be in the center of Scarterra deep underground yet somehow of infinite size. It is largely believed that the Elemental Plane sustains all life on Scarterra since all life is made up of some quantity of the four classic elements of fire, water, air, and earth. No mortal has ever visited the Elemental Plane and come back alive, so it is unknown whether there are separate realms for all the separate elements of the Elemental Plane is a single swirling morass of conflicting energy. While mortals cannot visit the Elemental Plane with magic, it is relatively easy to use magic to bring energy or creature from the Elemental Plane into the Material Plane. Most Invocation and Conjuration magic taps into the Elemental Plane at some level.