Acheron Acheron ( ÆTCH - ur - un ) was an Outer Plane in the Great Wheel cosmology model representing alignments between lawful evil and lawful neutral with emphasis on law . Some characteristics of this plane were ascribed to the World Tree cosmology planes of Clangor , Nishrek , and Warrior ' s Rest when that cosmology became popular . Nishrek and Warrior ' s Rest survived the Spellplague and became part of the World Axis cosmology model . Description . Acheron was the bridge between the ultimate order of Nirvana and the regimented evil of the Nine Hells and as such , each layer emphasized order over evil . The land masses on each layer were blocks of geometric simplicity the size of nations floating in a sea of air . The blocks would slowly collide and part without causing any upheaval or tremor , allowing beings to move to a new block if desired . The dance of the blocks was carefully orchestrated and creatures of high intelligence could usually discern a pattern for an area by studying the motions . It was said gravity pulled toward the center of the blocks but in practical terms gravity was normal to each surface . Avalas . Acheron was sometimes known as the " iron - shod battle planes of Acheron " due to the characteristics of the first layer , Avalas . The blocks of the top plane were black with a metallic hardness that allowed the sounds of battle and troop movements to reverberate loudly . Avalas had the most block - like worlds and the highest population as the armies of the Outer Planes spent their afterlife clashing in neutral territory over differences both subtle and gross . The landscape consisted of cone - shaped mountains and pits plus the iron fortresses of the various armies . The only other remarkable feature of this layer was the river Styx that would bubble up from one pit , meander across two or three sides of a block , and then disappear down another pit . The Styx did not visit all the blocks , but those it did could be reached by Charon and his servants . Avalas touched the Astral Plane and had spherical portals to the three adjacent planes : Nirvana , the Nine Hells , and Concordant Opposition . The portals hung at fixed locations in space and would pass harmlessly through the blocks , becoming inactive while inside a block and reactivating when they reappeared . Anyone emerging from a portal would start to fall toward the nearest block and almost certainly required some form of flight to avoid a high velocity impact . The portals were activated by touch and the destination could be determined by the sound it made when activated . A harmonious chord indicated a portal to Nirvana , a dissonant chord meant the Nine Hells , and silence indicated Concordant Opposition . Thuldanin . This layer was the , , and scrap heap for countless contraptions , creations , weapons , armor , failed experiments , broken devices , fallen buildings , and shipwrecks of sea and air . The blocks of Thuldanin were hollow and pockmarked with pits that lead to the interior a few miles / kilometers down . There the flotsam and jetsam of the ages turned to stone in a matter of days or weeks due to the magic of this layer . Thuldanin had no inhabitants , only the occasional visitor from Avalas looking for some piece of magic or technology that might turn the tide of battle . Tintibulus . The third layer of Acheron had blocks different than those of the other layers . Here the blocks were made of gray volcanic stone and the faces were six - sided , eight - sided , or even higher in number of edges . When the blocks of Tintibulus collided the surfaces would fracture along natural fault lines into hexagons great and small . This layer had no inhabitants but was attractive to magical researchers for its emptiness and isolation . Ocanthus . The blocks of the fourth and final layer were square and so razor - thin as to be almost two - dimensional . They ranged in size from a few inches / centimeters to several miles / kilometers across . Both sides of the hard black squares had normal gravity pulling to the surface and could be walked upon . Being hit by the edge of one of these razor - sharp squares could be deadly . Inhabitants . The main inhabitants of Acheron were the spirit legions occupying Avalas . They were made up of the spirits of human s , dwarves , halfling s , ogre s , and many other mindless soldiers who died in wars after forgetting their purpose ; those for whom war became an end in itself . The spirits would congregate with others of similar beliefs or alignment and form nations on the surface of a block . They would fight to control a block and then join forces to conquer another block when it came within their reach . Legion members who were slain in battle would return with full strength within 24 hours , ready to fight again . The orc and goblinoid spirit legions shared the same large block in Avalas and besieged one another regularly . Other creatures that could be found in Acheron were wandering imp s , rust monster s , achaierai , and occasionally devil s and modron s .