Acheron is the plane of Law and evil. It is an endless battlefield fought atop the corpses of titans. When a combatant in the endless war is killed, their strength and vitality is given to their foe. Petitioners who die in the battles of Acheron are brought back the next day, now fighting on the opposite side of their conflict.
Many armies of the Upper and Lower Planes have fought their battles in Acheron.
Unlike Ysgard, Acheron is about war, not heroics and adventure. Acheron is the grinding war, contest and victory.
Arrax is the highest deity residing in Acheron, the Chained Lord of War residing over the endless battles and enforcing his codes of war.
Geographically, Acheron is made up of an endless red sea, as the river Styx ends here and mixes with the blood of the slain, and of the floating carcasses of slain titans. These titans, slain long past, have decomposed so that their flesh has become ground and soil while their bones remain. Many such titan carcasses float in Acheron, the largest being that of the titan Ymir.
Above the skull of Ymir hovers the Crown of Ymir, on which lies the realm of Arrax and one of Acheron's few cities.