[Paradigm Shift] Planar Planning

This will hopefully be a repository thread for working on how the NEW planes will look! Here's an example:

Carceri, the Astral Prison
Magical Notes: No form of magical or planar travel can function within Carceri. Once a body is stuck there, they cannot escape without first traveling through a natural portal.

Carceri is a dismal plane. Whether or not it was hand crafted to serve as the dumping grounds of the multiverse is under debate. Composed of bleak spheres that float suspended in space, the layers of this plane are nestled inside each other like dolls. There is truly no escape from this awful plane. Contained therein are many of the multiverses eldest imprisoned creatures. Besides the few Primordials and Titans kept locked up here, there are enemies of every culture and trapped deities of every portfolio. Its upper layers are bathed in gloomy light that grows more stagnant and darker as one descends within the spheres. Travel between layers is strictly guided by the Gehreleth, the gatekeepers of this prison-plane.

The Gehreleth
The fiends that inhabit this plane as though it were their natural home have been impressed into service by all manner of Powers. They name themselves Gehreleth, but most creatures in Carceri know them as jailors, wardens, and watchers. They guard every snaking passage that wends its way down into a deeper layer and the only egresses back into the Outlands.

Notes for expansion
Need to come up with layers, things imprisoned here, and adventure sites.