Formed Millions of years ago this was designed, by the Ancients, as a prison for the Dark Entity known as Balor, in later years. For decades(in our perception of time) he remained in his prison until he broke free and reentered the world.
Ever since that day he has been breeding living creatures to enter his realm after death, tormenting nad manipulating there mind so there is nothing but vile darkness that comes from them. These are known by man as the Devils or the Dark Ones of Chaos. However this is not to get confused with the Demon Species who are very much alive even though they linger underneath the surface imprisoned and banished from the surface world.
Other then this religions explain more information on what this place can be and it holds as much truth as anything could.
