The cosmos, if it could be grasped by a mortal mind, could most easily be described by envisioning that above the mortal plane lies the Five Heavens, one for each of the Five Thrones of the Divine. Ruling over the heavens are the hierarchy of angels who protect the worlds from their fallen brethren and await the return of the gods. Far below the mortal realms lies the gaping maw of the Infinite Abyss and the Nine Hells, which hold the countless hordes of demons and the courts of the Dukes of Hell respectively. Coexistent yet separate from the mortal plane are the four elemental planes
Surrounding and separating all of this is the Astral Plane, the three-dimensional sea where all planes, mortal and otherwise, float like impossible islands. Dotting the astral plane are the enormous petrified bodies of powerful beings long dead, the cities of gythyanki, mindflayers, and others, and huge leviathans who sail the astral sea. In the center of it all is said to reside the Eternal City, neutral ground for all beings, from angelic to infernal, from elemental, to mortal.
At the far edges and beyond the Astral Plane lies the Infinite Void, home of Elder Beings who predate all of reality, and wherein some sages say the Entity which slew the gods still resides, dead, but who if awoken would unmake all existence.