Archimonde's Vengeance is an enormous crater located in northern Mount Hyjal, due west of Nordrassil. It is located roughly where the orc base stood at the Battle for Mount Hyjal, and the name suggests that Archimonde completely obliterated it on his way up the mountain.
Baron Geddon can be found in the middle of the crater.
Video Description: An enlarged Archimonde climbs Mount Hyjal and grabs onto the World Tree with his hands, as Furion watches from afar on a ledge. The Arch Druid raises the Horn of Cenarius and blows into it. The wind blows about the trees, as a few wisps appear. These turn into dozens as they race towards the World Tree. Before long there are hundreds encircling Archimonde as he focuses on the tree. He lets go of the it in near-horror as the wisps rush about his form, quickening in speed. Archimonde groans and clutches his stomach, but the thousands of wisps continue, and his body seems to burns a white-blue colour. From afar, we suddenly see an explosion come from the tree. The demon disappears in a sudden disintegration, and fire rips loose across the land over the trees, which are instantly incinerated. As the blue mist of his form evaporates, a shining explosion comes from the tree as we fadeout in whiteness. We fade-in to an approach of the bottom of the World Tree, as its roots grow once more from it.