Oroku Saki's afterlife (IDW)

Oroku Saki's afterlife is the place where his soul went before he was resurrected by Karai. It resembles an endless grassy plain, with a deep river or sea on one side, and a red or blue sky overhead. There is only one structure seen in this entire world: a medieval Japanese castle set on a rocky mountain, where the king of the afterlife dwelled.

It is unclear precisely what kind of afterlife this is. Saki described it as being the destination for all those who die, and their uniform fate to become shadows of their former selves, without purpose or autonomy. However, Tang Shen's presence and Donatello's near-death experience seem to indicate that this is not the case, and that his destination was only one possible place that dead souls might go.