The Void

A space of 'everywhere' beyond the universe. It has a cold, disturbing gravity to it when looking at it.
On exiting The Waters/ The Stem with the souls of both Oksana Bosko and Moonlight Through Rain, Qwyn broke through a barrier on the ocean's surface.
In doing so, they broke a chasm into the ocean, which drained the waters, ships, and at least some of the dead into this void space.
May be where The Tree is.