Fah'lrrg, often called the Demon Wastes in Common, lies north of the Eldeen Reaches by land and the Shadow Marches by sea. It is separated from the Reaches by the Shadowcrag Mountains, and a great natural labyrinth of stone, making it difficult to arrive there by land. It is separated from the Marches by the Crescent Bay, and sailing would seem a much easier traversal method, but the bay is littered with shipwrecks that suggest otherwise.
It is the most hostile environment on Eberron, and at first glance seems to be totally unable to sustain humanoid life. They are a blasted landscape, miles of volcanic basalt bleeding into rust coloured desert, toxic swamp and frozen tundra. Ancient ruins from the Age of Demons dot the landscape, destroyed by both time and dragons. It is a land suffused with fiends, not just the more dramatic demons one might envision, but malicious spirits too. These minor fiends lack a distinct physical form, and instead inhabit aspects of the land itself. Hellwasps are one way that these fiends manifest, but they can also manifest as plants that possess those who eat them, or they can dwell in bodies of water and animate it after it has been consumed. In the north, these minor fiends will possess and animate the corpse of any creature that dies. The Demon Wastes are not a natural environment, the land itself is evil, and actively malicious in a way that goes far beyond natural danger.
Despite all of this, life clings on. There are countless entrances to Khyber throughout the Demon Wastes, and whilst these allow fiends onto the surface, they also allow the unique life of these demiplanes to spread, where they can form localised ecosystems. It is because of this that the Carrion Tribes are able to survive, providing access to food and water.
Life and Society
Two distinct groups occupy the Demon Wastes. The Ghaash'kala clans who inhabit The Labyrinth, and the Carrion Tribes who struggle to survive in the Wastes. Both of these groups have existed in some form for thousands of years, though their exact makeup changes often, with tribes being destroyed and rebuilt repeatedly over the centuries. Evidence suggests that even the Ghaash'kala have been fully eradicated at least twice, only to be reformed by those who hear the call of Kalok Shash.
The vast majority of the Carrion Tribe population in the Demon Wastes today is made up of the human descendents of refugees from Ohr Kaluun in Sarlona who were fleeing the Sundering. They got shipwrecked off the coast, and when they tried to leave by land they found their way barred by the Ghaash'kala, trapping them in the Wastes. There have been tribes of many species throughout history, however. The original Ghaash'kala primarily fought against corrupted orcs and gnolls, and there have been notable tribes of dwarves, shifters, goblins and even halflings. Many of these people became stranded in the Wastes in the same way that the Sarlonan refugees did, but others arrived via Khyber.
No matter what happens, there is always a significant population in the Demon Wastes. Whenever the population gets too low, something occurs to bolster it back up. The Overlords love their toys, after all, and it wouldn't do for them to be bored.