Rumored to be in the Northern Hinterlands.
Sulyott confirms that it is held in Ogenheim, Kiridin, Northern Hinterlands, one of the barbarian lands. Currently possessed by Nightcloud, one of the 3 so-called furies.
See the log Civil War, Barbarians, and Other News for the initial report. It was sent by Minischmee while he was King of Bizantium