Nine Hells

The Nine Hells (Lawful Evil).
Nine subplanes, each presided over by a powerful devil. These devils are not so much lords as they are regents or controllers. They rule only by permission of Asmodeus, who controls the 9th level of Hell.
Devils travel between the layers relatively freely, doing work where it's needed. Most of this work involves torturing, breaking and reforging souls into devils, tools or soul fragments but hey, it's a meritocracy and an efficient one.
It's not the strong who rule, but rather the brightest, cleverest and most forceful. It's not at all uncommon to see a lower class of devil lead a battalion, as it is a place where physical form plays second fiddle to the intelligence to use what you have. The main themes are domination, suffering, industry and industrially produced suffering.
Attached to the layers are the domains of the gods. Hecate's castle is tethered to one layer
Cool, but why would you want to go there? If you're really powerful and clever enough to know how to use that power, you too could rise to the top. You could live in a palace full of slaves with armies at your command. To a certain kind of person who values power and thinks highly of themselves, this may be paradise.