The first layer, Avernus, is a vast charred wasteland of rubble over which the iron towers of the Dukes of Hell stand. Legions of devils march across the plains in continual readiness for the next battle of the Blood War. A red light suffuses the sky and huge fireballs fly across the layer, randomly exploding wherever they hit. Beneath the blood-red sky balls of fire burst unpredictably. They are said to be embodiments of the rage of the imprisoned Lord of the First, Zariel.
The River Styx flows through this layer, as does the appropriately named River of Blood. From the gate in Ribcage the nearest site is the ruined city of Darkspine, where refugees desperately try to avoid the baatezu thought police while trying to do enough good to shift their town back to the Outlands.
The Bronze Citadel is a huge fortress city, housing massive numbers of devil troops and war machines. It is constantly being added to in the form of new fortifications against attacks. Lord Bel, formerly a powerful pit fiend before his ascension to noble status, is the current ruler of Avernus, having betrayed the former lord, Zariel, to obtain the position. He resides in a personal fortress at the center of the Bronze Citadel.
The largest series of astral conduits on Baator lead to the Maggot Pit, a sea of squirming infernal larvae, beyond which the Dragonspawn Pits of Azharul sprawl in a cluster of tall hills and mountains. Tiamat, the five-headed deity of evil dragons, stands watch over the way to the next layer with her draconic and abishai servitors. Nearby exists the Pillar of Skulls, a hideous landmark of trophy-skulls of those killed in the Blood War that reaches a height of more than a mile close to the entrance to the second layer.
A number of godly realms exist on Avernus, including Draukari, realm of kobold deity Kurtulmak, goblin deity Bargrivyek’s deceptively titled realm of The Peacable Lands, and Abthalom, the Nether Reaches, realm of dragon-queen goddess Takhisis. Vast legions of abishai serve the Queen of Darkness, milling through the Rallying Grounds and near the Temple of Takhisis and the Tower of High Sorcery. The towns in Draukari, hidden in the hills, mountains, and deep forests of the realm, are Frekstavik, Nibellin, and Snjarll. Kurtulmak’s realm is often raided by goblins serving Bargrivyek.
A number of unique devils cast from the hierarchy of the Hells also dwell on Avernus. Known as the “rabble of devilkin”, these exiles number roughly 50 former consorts, dukes, vassals, and other unique devils who lost favor with their masters. To prevent them from being summoned, they have been stripped of their names.