There are multitudinous layers of the Abyss, perhaps even an infinte number.
No one has ever cataloged them all, and its doubtful that any of the plane’s
natives, let alone any other bean counter, has ever considered the effort
worth the time and danger. Plain and simple, no one’s ever done so because
each layer is so horrible grotesque that a berk would have a barmy to want
to see any of them . Even fewer sods have the power to actually do so
and survive. For one thing, almost every layer of the Abyss is so
inhospital. For another, this plane is home to the tanar’ri, one
of the two races locked forever in the infernal Blood War – and they aren’t
particularly hospital either.