It is mentioned in several sources, but I can't seem to locate it. Presumably the seat of the Lunar Empire's Vampire Legion, which might be connected to the Vampire Legion of Tanisor?
Note: In TotRM 19 it is implied that the "Vampire Kingdom" borders the Lunar Empire in northern Peloria.
..and the Sourcebook says they are rumored to 'train in the mountains'. (the Pavis book for HeroQuest further states that they 'train in the mountains of Peloria').
I doubt if these are the Yolp Mountains or Blue Moon Plateau because they are troll country, which leaves the Western Reaches/Carmania, Doblian, the Jernalf Mountains (I think this one is unlikely because the Jernotians wouldn't stand for it), Ford, or maybe Imther (I am dubious about those). If there's a connection to Dorastor... maybe the Tobros Mountains?