Avernus is the first layer of Baator and 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.
The first layer of Baator is a wasteland of charred, rubblestrewn plains, with mountains and talus-sided foothills breaking up the monotony. Legions of mail-clad devils are on perpetual watch here, always assembling for some new cross-planar Blood War sortie. Blood-red light suffuses the air, and fiery balls flit randomly across the sky, sometimes detonating to terrible effect. Travelers not protected by artificial structures or caves are 10% likely per day to find themselves at ground center of a fireball dealing 6d6 points of fire damage (as if cast by a 6th-level spellcaster). Runnels of blood flow in streams across Avernus, finally joining the River Styx. The origin of the blood is unknown, though the devils say it is likely the blood of all Avernus's past victims.
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.
Lord Bel, a powerful pit fiend, 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 Pillar of Skulls is a hideous landmark of trophy-skulls of those killed in the Blood War that reaches a height of more than a mile. It is very close to the entrance to the second layer, Dis.
- The largest series of astral conduits on Baator lead to the Maggot Pit, a sea of squirming infernal larvae.
- Dragonspawn Pits of Azharul sprawl in a cluster of tall hills and mountains.
- Garden seems to be an oasis, with fountains of delicious water and trees that put Arborea's to shame. Many are the explorers who brave the terrors of Avernus in the chance of finding it, but many of those who do are never heard from again. Is the Garden a refuge for souls that reached Baator by mistake, a lost paradise hidden by the gods, or a sinister lie?
- Abthalom, the "Abyss" of 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.
- Draukari, the realm of the kobold god Kurtulmak, who is said to be a brother or son of Tiamat. 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, whose own realm "the Peaceable Lands" is nearby.