High up in Zirakzigil, there lies a cave. This cave was a means to harness the light of the sun and bring it down to the depths of Moria. Years of neglect have brought this system to its knees, and now the cave is home to merrevail, Wargs, and other dark creatures.
You should defeat the morroval-queen, Ergoth while she is at her strongest. If you weaken her first, you will not be able to claim the greatest of rewards.