Acheron is an eternal battlefield of endless conflict. It is a plane of law where conformity takes precedence over any thoughts of good. Unending battles take place across the entire plane between huge armies, with no chance of victory or cease-fire. Each layer of plane consists of a huge numbers of iron cubes of varying size, from continent-sized to small islands; not all of these are actually cube-shaped, but they are generally called cubes nonetheless. The cubes float in an air-filled, infinite space, occasionally colliding with each other. Every cube face is habitable, with gravity always being directed towards the cube’s center; furthermore, the cubes are filled with caverns and tunnels.. The light on Acheron varies between that similar to bright moonlight to that of a dark and cloudy day. The sound of battle resonates around the plane and can always be heard in the distance.
As with other outer planes, Acheron is spatially infinite, consisting of four infinite layers or sub-planes. Acheron’s first layer, Avalas, shares borders with the neighbouring planes of the Nine Hells of Baator and the Clockwork Nirvana of Mechanus; travel is possible between Acheron and these planes at certain locations.
Acheron has four known layers:
The first layer of Acheron, Avalas, is also called The Battlefield. It contains the highest density of metal cubes and is thus host to the most fighting on the plane. The cubes are dotted with fortresses and covered with battlefields. Collisions between the cubes causes them to break apart in to smaller cubes, hence the smallest cubes are the oldest on the layer. The realm of Nishrek, a separate plane in the 3rd-Edition Forgotten Realms cosmology is located on Avalas. It is home to the orc deity Gruumsh and the other deities of the orc pantheon including Bahgtru, Ilneval, and Luthic. Bralm’s realm, the Hive Fortress, is in Avalas. The citadel of Scourgehold is the realm of Hextor, the god of tyranny and half-brother of Heironeous. Here Hextor presides over his legions as they train in The Great Coliseum. Clangor, another separate plane in the 3rd-Edition Forgotten Realms cosmology is located here. It is the realm of goblin deities Maglubiyet, Khurgorbaeyag, and Nomog-Geaya. Avalas also contains the realms of Amatsu-Mikaboshi (The Brilliant Land) and Lei Kung (Resounding Thunder). With the destruction of Iyachtu Xvim, Bane has returned to his Black Bastion, a massive fortress-castle on the layer.
Compared to Avalas, Thuldanin has a relatively small population. Geographically it is very much like the first, consisting of numerous huge cubes. On this layer the cubes are scarred and pitted by battle. Many pits lead down to labyrinths containing the refuse of the endless battles of the plane. The remains of broken war machines and other devices line the interiors of the cubes, even some finely crafted weapons can be found amongst the rubble. Thuldanin has a preservative quality that results in the petrification of objects and creatures that spend too long on the layer; savvy visitors spend no longer than 29 days here. The realm of Hammergrim, a separate plane in the 3rd-Edition Forgotten Realms cosmology is located on Thuldanin. It is the realm of the duergar god, Laduguer.
Tintibulus contains a large number of four-sided, five-sided, eight-sided, and other solids in preference to the six-sided cubes that predominate the other layers. A layer of thick dust coats the surface of the solids here, which are made of a grey volcanic stone. Magicians’ libraries are scattered here, and is the best place in the Multiverse for magical research.
The fourth layer contains no regular shapes, but many shard-like solids of black ice with razor sharp edges. The shards fly about in violent motion, referred to as a bladestorm. At the extreme of Ocanthus lies the Cabal Macabre, the realm of the goddess of death and magic, Wee Jas. Her domain takes the form of a huge and intricately carved ice castle, that glows with a pale light. Wee Jas’ powers quell the bladestorm within a half mile of her location, allowing her to maintain her realm. Cabal Macabre is located on a huge, possibly infinite shard of black ice which may be a barrier between Ocanthus and a deeper level of Acheron.