At the height of the Codominium, a Khuzan clan adapted part of an existing natural cave system for use as a hunting lodge. Each autumn, the Khuzdul would travel there to spend a month hunting; the rest of the time the site sat empty. It has remained hidden for more than a millennium.
UPDATED: Mining, Abandoned Mines, and Natural Caves; three aspects of the underground that players may explore during their adventures. HM3 Encounter tables to randomly generate encounters.