The Abyss

The Abyss is the lowest of dimentions, below even Hell, and strecthes down infinitely.

Bottomless Prison
The Abyss is where Sattanael and the Betrayers will be cast during the Millenium. Afterwards he will be released for one more Attempt. Then he will be cast into Hell at the End of Time.

It is a bottomless absense of light, heat, and laughter. It can be escaped, but it takes extremely long time. This is why The Betrayers will be there for a thousand years; not locked but trying to escape.

History
The Abyss is known about by all and feared nearly as much as Hell. However it is not the fate for any spirits but the highest of the demons and will not be the eternal fate for any. Instead of a created dimention, it is rather the end of creation, and thus goes on infinitely.