We're not told the precise location of Ost-in-Edhil, the chief city of the Elves of Hollin. We do know that the road to the city from the West-gate of Khazad-dûm ran along the Sirannon for at least part of its length, so it seems reasonable to assume that the city probably lay somewhere on that stream, as shown here. It may possibly have stood on the larger Glanduin into which the Sirannon flowed, or elsewhere on the plains westward of the Misty Mountains, but it was clearly relatively close to Khazad-dûm.