The Storm Pit is the third and final Invasion dungeon, accessible through a red portal in the Realm of Lies. It is home to the Ascendant Riftwalker, the most powerful of the three Riftwalker bosses.
Lore
Once again a Riftwalker has bridged the inscrutable distances between the Mortal Plane and its esoteric dimension, anchoring its presence to Sanctuary. The arcane beacon that guided the dreadful invader was none other than that of Belial, the Lord of Lies. The Lesser Evil, exiled from the Burning Hells, now dwelled with his wicked servants in a cave beneath Harrogath, in the recesses of which a portal has opened. It leads to a gaping furnace where occult energies and boundless malice mingle to strengthen the Ascendant Riftwalker cruel determination.