Wherein the Guvners recount the names of those layers from whence successful expeditions have returned...

Popular lore puts the number of layers of the Abyss at 666 but whether this is just screed or fact, the true dark is unlikely to ever be revealed.

1 - Pazunia; also known as The Plane of Infinite Portals
2 - Driller's Hives
3 - The Forgotten Land
4 - The Grand Abyss
5 - Wormblood
6 - Realm of a Million Eyes
7 - Phantom Plane
8 - The Skin-shedder
9 - Burningwater
10 - “That Hellhole”
11 - Molrat
12 - Twelvetrees
13 - Blood Tor
14 - The Steaming Fen
17 - Death's Reward
21 - The Sixth Pyre
23 - Iron Wastes
27 - Malignebula
32 - Sholo-Tovoth: The Fields of Consumption
45 to 47 - Azzagrat
49 - Shaddonon
52 - Vorganund
57 - Torturous Truth
66 - The Demonweb Pits
67 - The Heaving Hills
68 - The Swallowed Void
69 - The Crushing Plain
70 - The Ice Floe
71 - Spirac
72 - Darklight
73 - The Wells of Darkness
74 - Smaragd
77 - The Gates of Heaven
79 - The Emessu Tunnels
88 - The Gaping Maw (or Brine Flats or Abysm)
89 - Shadowsea
90 - The Guttering Cove
92 - Ulgurshek
111 - The Mind of Evil
113 - Thanatos
128 - Slugbed
137 - Outcasts' End
142 - Lifebane
148 - Torrent
176 - Hollow's Heart
177 - The Writhing Realm
181 - The Rotting Plain
193 - Vulgarea
222 - Shedaklah (aka The Slime Pits)
223 - Offalmound
230 - The Dreaming Gulf
241 - Palpitatia
245 - The Scalding Sea
248 - The Hidden Layer
274 - Durao
297 - The Sighing Clifs
300 - Feng-Tu
303 - The Sulfanorum
313 - Gorrison's Grasp
333 - The Broken Scale
340 - The Black Blizzard
348 - Fortress of Indifference
357 - The Arc of Eternity
377 - Plains of Gallenshu
399 - The Worm Realm
400 - Woeful Escarand
403 - The Rainless Waste
421 - White Kingdom
422 - The Seeping Woods
423 - Galun-Khur
452 - Ahriman-abad
471 - Androlynne
487 - Lair of the Beast and Mansion of the Rake
489 - Noisome Vale
493 - The Steeping Isle
499 - Carroristo
503 - Torremor
507 - Occipitus
518 - Melantholep
524 - Shatterstone
531 - Vudra
558 - Fleshforges
566 - Soulfreeze
570 - Shendilavri
586 - Prison of the Mad God
597 - Goranthis
600 - Endless Maze
601 - Conflagratum
628 - Vallashan
643 - Caverns of the Skull
651 - Nethuria
652 - The Rift of Corrosion
663 - Zionyn