Bósi reports that a relic of Gorothúl's lies among the Water-wheels of Nalâ-dûm and will require careful usage of the mechanisms to reach and destroy.
Bróin believes that one of the relics Gorothúl left behind in Moria was given to the merrevail infesting the Mirror-halls of Lumul-nar and wants you to destroy it.
Defeat Caerlûg, the foul creature that has taken residence in the depths of the Water-wheels of Nalâ-dûm.