Descent into Hell!!! Rarrr!...Well, sort of...

[Lalwendë]

Originally Posted by Lush

But what is the ultimate hell in Tolkien's creation? Is it, in fact, Mordor? Or does an ultimate, metaphysical hell even exist?

I think it possibly does, certainly for Saruman:

To the dismay of those that stood by, about the body of Saruman a grey mist gathered, and rising slowly to a great height like smoke from a fire, as a pale shrouded figure it loomed over the Hill. For a moment it wavered, looking to the West; but out of the West came a cold wind, and it bent away, and with a sigh dissolved into nothing.

This is quite a horrific image, yet so simple and wholly unbloody. Here is one of the Istari who by rights ought to return to the west after his death, yet he is simply blown away to nothing. It is perfect, poignant and seems utterly final.