Purgatory is a concept found in various religions around the world that is midway between the eternal punishment of Hell and the unending paradise of Heaven, it exists to purify the souls of those who are deemed too sinful to be admitted directly into Heaven but not evil enough to be condemned to Hell.
Purgatory consists of temporary punishment for those involved, but unlike many versions of Hell the ultimate result of Purgatory is to be set free and enter the Kingdom of Heaven (or a similiar concept). This realm is also said to be governed by Il Separatio, who is the separation of the light and dark when God created the universe out of the darkness. This is due to the fact that Il Separatio is entirely neutral in the endeavors of the Natural Order.
Purgatory is infact, a realm where monsters are sent to endure eternal damnation instead, and even the humans whom are considered monsters as well. It is also revealed that across the far reaches of Purgatory, which is said to be uninhabitable by any known monster no matter how strong, lies the Great Old Ones whom were the very beings that predated or existed during the formation of the universe.
While many of them exist within Purgatory, few other Old Ones still roam or are imprisoned within other dimensions by beings whom are not associated with God.