Acheron is made of immense iron blocks whose metallic surfaces ring beneath the marching feet of endless armies. These blocks drift through an airy void, sometimes colliding with a fearsome clang, crushing all between them and sending shudders through the plane.
Acheron has four layers, with the largest blocks gravitating to the top layer. Some scholars have theorized that the crashing blocks of the upper layers are eventually broken down into smaller chunks of matter that sink to the lower layers. The truth is actually the opposite: the tiny shards of Ocanthus, the lowest layer, break off from an icy mire in its deepest recesses and are gradually assembled and organized, perhaps under the influence of nearby Mechanus, into the perfect cubes of Avalas.