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Below the splendor that is Edden Prime, lies an entire reality of cavernous landscapes that abound for thousands of miles. Layered ten strata deep are the levels of Sub Edden, where each level is a hallow region between arched layers of nanogabbro diabase stone twenty miles thick that were formatted in a lattice structure by Helvestus the sacred demiurge of the Dwarven people.
These hallow cavities, though void of luminaries and dark with grey stone walls, are abundant in the ambient light that passes through the several dozen vertical shafts which run from the surface mountains down to the very edge of Sub Edden where lies the open air above Kyia.
Outside of these well lighted regions surrounding each successively lower aperture in the stone ceiling above, are many bioluminescent mosses and fungi. There is also a considerable amount of weather patterns that diffuse light throughout these many layers of stone and earth, as lightning dense clouds drift up and down through shafts and ravines.
Here in this labyrinthine world of supermassive tunnels and caves, used to live the Vivaltren peoples, an equally large race of polymorphic beings that once numbered in the hundreds of millions. Though after prolonged conflict with the Dwarven peoples above, much of Sub Edden was conquered by the Casmarians, and a permanent Dwarvish presence was established.