Storm, Twilight and Hammer

The Stormreaver Clan was not composed solely of orcs from the Shadow Council, but also included the ogre magi who served under Cho'Gall. While a questionable ally, Gul'dan kept that two-headed buffoon as close as he could. I do wonder if the reason was that he knew they would one day betray each other in their lust for power.

Alas, one failed while the other lives?hiding beneath the sands, behind the cloak of a cult that worships myths and legends as old as this world. I have taken the liberty of making the succubi share their plans with me. To the west, past the cave where you defeated her, you will find the Windrock Cliffs. It is there that a member of the Twilight's Hammer holds a fragment of the key. Slay him and return with whatever you find.

The lockbox merely contained the first fragment.

Both fragments together will now serve as the key to enter the ruins of the castle. Beware, for you will face both servants of the Legion and cultists of those long forgotten.