The Inescapable Prisons of Carceri (or just Carceri) is the neutral-evil outer plane of punishment. It is notable for being immune to traditional plane-jumping energies, and for having very few (if any) ways of escape, outside of a Wish spell.
About
Carceri sits between the hoplessness of Hades and the Madness of Pandemonium, and the depression of these neighboring planes seeps into and mingles with Carceri, making it the most emotionally punishing plane in existence, alongside it's physically unbearable atmosphere.
Carceri is not linked to the other Outer Planes traditionally, and can not be accessed or departed from by means of Plane Shift, Gate, or other typical magics. However, it is still possible to stumble upon a colored pool in the Astral Plane that traps the poor soul in Carceri (with no way out).
Layers
Agathys
Agathys is the deepest (and final) layer of Carceri. It is described as a dark sphere of black ice, where the wind howls endlessly, and little light or shelter can be found anywhere. The void echoes with the sound of shifting and breaking ice, combined with the crushing agony of petitioners' souls frozen within the black sphere.
Notable Locations
The Library of Ignorance
Located in Agathys, The Library of Ignorance houses a madman named Dreschm who spends eternity forgetting and remembering various elements of the universe, and trapping those elements on page with a dark magic, creating an unbelievable artifact known as The Book of Knowledge. Occasionally, Dreschm takes pages out of the book to refuel the lone fire that keeps his library warm.
Despite being called a library, the innumerous shelves inside the building are completely barren.
The Library has four exits, which do not work. However, there is a secret escape. Escaping the Library allows the brilliant scholar who deciphers the clues to teleport out to any other plane of their choosing, one of Carceri's very few (and very hidden) escape passages.
