The Realm of Chaos is the deepest and most terrible region of the Warp, the domain where the Dark Gods themselves hold court. It is not a place of fixed geography but a landscape sculpted entirely by emotion and belief, its impossible vistas expanding, folding, and reforming according to the moods of the powers that dwell there.
The realm is divided into the domains of the four great Chaos Gods, each a reflection of its master's nature. Khorne's lands are a brass-walled battlefield heaped with skulls; Nurgle's a rotting garden teeming with pestilent life; Tzeentch's a labyrinth of shifting crystal and impossible geometry; and Slaanesh's a palace of unbearable excess. Between them sprawls a contested no-man's-land where the boundaries blur and the gods' endless war spills over.
Mortals cannot walk this realm in body, only in soul or spirit, and few who do so return unchanged. It is from here that daemons pour forth, that the Chaos Gods scheme against one another, and that the corruption of Chaos flows into the material universe. To the damned it is paradise; to all others it is the final nightmare toward which every warp-storm and every whispered temptation ultimately leads.