Khyber is a massive subterranean realm that is filled with fiends, aberrations, the daelkyr, bound overlords, and other monsters. While the upper layers of Khyber are stone and dirt, the lower levels are a vast array of demiplanes with all sorts of strange contents.
Khyber is an alien world sprawling beneath the lands and oceans of Eberron, a labyrinth no surface dweller can hope to fully map. Its twisting tunnels and vast caverns defy reason, hiding designs that only madness could create. Great chambers serve as pastures for monstrous creatures, while immense chasms shelter forgotten cities carved or grown from the rock.
Deeper beneath the surface lie horrors from ancient epochs, bound since the Age of Demons. Overlords remain imprisoned in dragonshards or arcane cells, while the daelkyr, remnants of Xoriat's invasion, carve out their own warped kingdoms. Mind flayers and aboleths stalk these depths, commanding thralls and dreaming of dominion over the surface. Khyber’s depths are a breeding ground for unspeakable plans, as its denizens seek to shatter the sunlit world and plunge it into endless chaos.
In the deepest reaches, Khyber twists reality itself. Its laws are not those of Eberron; colours unseen by human eyes glow from alien crystals, rivers of molten stone defy physics, and darkness becomes a living, oppressive force. Here, the very essence of the world warps, creating a realm of madness and wonder, an endless domain where nightmares roam and the eternal dark reigns supreme.