Nurunkhizdin was located under the high central peaks of the Eastern Hills.
Founded by the exiled king of the Ironfists - Buldin and his faithful ones in S.A. 2797, when the majority of the house would not have any more dealings with him and his followers due to the latter’s open friendship with Sauron.
It continued to serve as the royal seat (though not the population centre) of Sindri’s people until T.A. 58 when all contact with the mansion was lost. At this time the unknown evil touched Nurunkhizdin and messages about renegades ceased. Sindri's ring disappeared from all knowledge.
The remainder of the house did not investigate why and when Nurunkhizdin passed into oblivion.
Eventually Sauron came to the city of Nurunkhizdin and took the First of the Seven rings back from Buldin's descendant.
References[]
Ref.: Other Minds magazine, issue 4