Nether

Nether is not a realm in truth. Nor is it accessible to the average mortal. It is a place wedged between the corporeal world and Ruin, where restless spirits are forced to roam. There are three known ways for a spirit to leave Nether:

Plucked away by Celestials of a God, anchored to the corporeal plane via sorcery, or dragged through the barrier into Ruin, to be made sport for demonic entities...

Nether acts as a buffer - a protective veil - keeping the beings of Ruin from spilling into the mortal realms. Alas, on occasion tears can be opened, acting as gateways, bypassing this defensive plane.