The Chaos Wastes
The Chaos Wastes have naturally high levels of chaos corruption.
The Wastes lie near the Goromandy Mountains and Gianthome Mountains. The Chaos Wastes technically border the Northern World's Edge Mountains, however to get to the settlements of that province, an army would have to travel a long way through the Eastern Oblast and Southern Oblast.
The Chaos Wastes are a frigid, inhospitable wasteland in the far north, beyond Norsca. The Chaos Wastes lie close to the northern Chaos Portal, source of magic in Warhammer. As a result of the raw, chaotic magic and warpstone dust, the region is changed - rifts of lava open up in the ground, time flows in strange ways, mutant creatures prowl the land and mountains twist themselves into strange shapes.