Bowels

The Bowels are the foundation of the plane of the mortals, the very interior of their world. These are dark and endless halls of caves, dim lighted and erupted landscapes, smacked against the interior side of the boundaries of the sphere. The size of the Bowels reaches over entire continents, full of deformed landscapes, rocky exteriors and volcanic ruptures. Many hideous and horrible creatures live in these dark halls, causing terror and death upon many that were locked down there.

(Just the bit about how the Bowels are the foundation of the Earth needs clarification. It's rather magical. You would not end up in the Bowels by digging a deep hole through the Earth. The Bowels exists as a magical realm within the Earth.)

The Bowels is where the souls of the mortal races went when they died. Following the imprisonment of Tzarrists in the Bowels, this became the source for morality among mortals. The ones who lived bad were condemned and sent to the Bowels for endless torture and experiments by the imprisoned Gods, while the ones considered to have lived a good life were sent to the Havens to live in peace and harmony.

The Bowels were ruled by the Gods who were driven down there and locked behind its gates for being in favor of experiments of the mortal races, Gods such as Xrysmathra, Yurixryz, Bizmuth, and Sulphira. Many wars were waged in between those Gods, causing their experimental races to harden and strengthen themselves. Many lesser Gods were also killed during these wars in the Bowels, only to strengthen the stronger ones.

Deep inside the Bowels, in the Pool of the Forgotten Souls, where the condemned souls went, Xrysmathra manipulated and created new races with the aid of Yurixryz. She built great magical barriers around these pools, preventing the other Gods from entering and drawing their powers from the source, ultimately making her followers outnumber any other God's forces, resulting in many Gods looking at her as their worthy leader. Even though no one objected her ruling, Xrysmathra waged war upon other Gods and races, only to regain more power so that she could breach the gates of the Bowels. She became the clear ruler of the Bowels, taking of the title 'Xrysmathra of the Bowels'.

Eventually as her power grew and her forces grew stronger from the endless wars within themselves, she managed to create cracks on the Gates that had locked them inside for centuries. Her greatest ally, Yurixryz was able to use his shadow magic and slowly corrupt the mortal races at the Gates, causing them to turn on each other and weaking their own defences of the gates severely. Yurixryz also turned the mortal races on the Havens, making their support from them reach an absolute low. As the mortal races waged war upon themselves and the defences of the Gates of the Bowels were weaken, Xrysmathra used her manipulation over soil, earth (and stone to a certain degree) to create a bridge in between the Bowels and the plane of mortals, where her forces assaulted the gates and eventually breachied them. Her experimental races now spilled inside the plane of mortals, slaughtering the races upon the earth, leaving but only a few remaining survivors who were forced to flee to the brink of the world. Xrysmathra enslaved the mortal races, taking complete control of the plane of mortals.

During the Turn, the gates of the Bowels were but a battle field between the two factions, the areas around it becoming nothing but wastelands again, endless mortals and Gods descending into oblivion. At the end of the Turn, many of the Gods who broke free and survived the wars were locked inside the Bowels again, imprisoned in despair and agony once more.

Later, after the Treachery, Xrysmathra opened the gates of the Bowels again, making it her main source of power, where she drew unbound power from the lost souls and sent Gods who she enslaved into imprisonment and slowly corrupted them to follow her cause.