Malbolge, the Crushing Lands, is the sixth hell of Baator, a place of craggy, black stone and ash filled with stinking vapors, smoke, fire pits, and huge caves and caverns in which ancient baatorians still lurk. The air is hot and choking, and the whole layer exists at a steep tilt so that no flat terrain exists. Falling is a constant danger here, as are rockslides and avalanches.
The nobles of this Layer dwell in copper fortresses, whose metal plating helps ward off the worst of the falling stones. The mysterious Hag Countess travels between these fortresses in disguise, testing the gentility of her subjects; she doesn't want mindless brutality, and destroys those who commit it.
Malbolge is a noisy place populated by tormented lemures, cornugons, and the occasional Spinagon. The layer was once ruled by Triel+the+Fallen until the Hag Countess took it from the Lord of the Flies' vassal Moloch.