According to the Book of the Drastic Resolutions: Darkness the Uz organize the Underworld in Seven Hells:
First Hell, aka Dark Waters, ruled by Adzurana
Second Hell, Realm of the Mother Night, ruled by his son Argan Argar
Third Hell, aka Waiting Ground, Grey Hell, Outer Womb, ruled by Zurgoteg, the Darkness within Earth
Fourth Hell, aka Inner Womb, is the Troll Paradise, ruled by Kyger Litor
Fifth Hell, aka Burning Prison, Bright Hell, where the Enemy Bright Eye goes every night
Sixth Hell, aka War Hell, ruled by Zorak Zoran
Seven Hell, aka Ratslaff's Rocks, Boggle Range, Rokotor's Dungheap, Disorder Deep, Uncertain Realm, the last stand against chaos. The gateway at the lowest part is called Arrquong
Beyond the Seven Hell is only chaos
It's uncredited, but may be from Greg.