From WoWWiki

The Master's Glaive is located in the southern parts of Darkshore. It is the site of an enormous skeleton forgotten one^{DF 145} cleaved through the head by an immense sword. To the west of Darkshore stands a mysterious monument, a massive adamantine glaive buried in an unmovable boulder called the Old God Skull. The night elves consider this a sacred area, as they believe the mysterious titans, creators of the world, are the only ones who could have wielded the gigantic glaive.^{WRPG 194}

A popular theory is that this is the place where one of the Old Gods fell to the might of the Titans. Onu refers to it being where an "old lord of the earth" fell long ago in the quest The Master's Glaive.

The sight of the Master's Glaive is awe-inspiring, which is precisely why the Twilight's Hammer have chosen it as a location for one of their dark altars. This cult worships the Old Gods, and they may be attempting to reawaken the remains of the dead god to let it roam the world once again. A prominent theory is the idea that removing the sword may allow the Old God to regnerate, since why would the Titans leave a weapon that was capable of killing an Old God in the Old God's corpse if there wasn't a good reason?

There are rumors of a complex underground labyrinth underneath the remains.^{DF 145}

Subzones of Darkshore
Ameth'Aran • Auberdine • Bashal'Aran • Blackwood Den • Cliffspring Falls • Cliffspring River • Grove of the Ancients • The Long Wash • The Master's Glaive • Mist's Edge • Remtravel's Excavation • Ruins of Mathystra • Tower of Althalaxx • Twilight Shore • Twilight Vale • The Veiled Sea • Wildbend River