Coldharbour is a realm of http://www.uesp.net/wiki/Lore:Oblivion created and ruled over by http://www.uesp.net/wiki/Lore:Molag_Bal, the http://www.uesp.net/wiki/Lore:Daedric_Princes of Domination. It contains an apocalyptic version of http://www.uesp.net/wiki/Lore:Nirn; the sky is on fire, the ground is a barely-traversable sludge, and the realm is filled with ancient, blackened ruins. A defiled copy of the http://www.uesp.net/wiki/Lore:White_Gold_Tower exists, splattered with blood and excrement.
The realm is desolate and barren, filled with suffering. It is unnaturally cold, even with magical resistance. The air assaults the senses, changing rapidly from rancid death to sweet flowered perfume.
http://www.uesp.net/wiki/Lore:Coldharbour