Azzagrat

From Fiendish Codex I: Hordes of the Abyss (3.5e):

The chattering markets and writhing pleasure palaces of Azzagrat draw visitors from around the Great Wheel. They come seeking obscure magical lore or perverse delights unavailable elsewhere, confident in the safety of the most germane society in the Abyss, where even demons present a veneer of civility and courtly comity. But for all its reputation for safety, Azzagrat holds just as many dangers as any layer of the infinite Abyss - and perhaps a good deal more.

The Triple Realm of Azzagrat consists of three distinct layers woven together by the demon lord Graz'zt, the Dark Prince of tyranny and despotism who controls the largest empire in the Abyss through a combination of fear, political manipulation, and cunning intelligence. The inhabitants of Azzagrat obey the will of Prince Graz'zt because their fortunes rise with his, and because he has eliminated all disloyal inhabitants of his realm over the course of generations.

Azzagrat's markets boast a staggering variety of products, services, and exotic slaves surpassing anything available in the Abyss. Graz'zt himself profits greatly from this business, and by the Dark Prince's personal decree any merchant bearing his six-fingered sign is to be considered safe from harassment from the inhabitants of the layer. Thievery is bad for business and is not tolerated under any circumstances (although a good deal of it goes on without the knowledge of the authorities).

The theme of Azzagrat is one of hidden danger beneath a cosmopolitan surface. The layer's cities are all like mazes, and its forests are intractable and full of shadows and lurking killers. If Azzagrat at first appears safe, it does so only to draw you in.

Everything on Rauwend, the gloomy 45th layer of the Abyss is somehow doused or subdued, taking on an equally gray pallor. All Move Silently and Hide checks made on the layer gain a +2 circumstance bonus, but because the place does not live long in one's memory, all Knowledge (the planes) checks concerning the layer take a -4 penalty.

Sunlight rises up from the ground of Barogûnd, the 46th layer, where shadows rise like dark columns far into the sky, which is dark by day and gray at night.

A wan cerulean sun feebly illuminates the dark sky of Voorz'zt, the 47th layer, where cold is hot and hot is cold. Flames glow blue and deal cold damage, whereas blisteringly cold gales cause fire damage. The magical properties of the layer reduce fire resistance by half. The layer can be reached only by way of Azzagrat’s other layers and has no connection to Pazunia.

Three things bind the layers: massive ovens of green flame that serve as gates, the River of Salt, and the triple-city of Zelatar, which exists simultaneously on all three layers.