The Dust of a Titan - Act 4 Side Quest

Start Location: Upper City of Lost Souls
Quest Location: The Fair Plains
Objective: Obtain the Ashen Powder
Reward: 2 Skill Points + Experience

The Dust of a Titan is a Side Quest that begins in the Upper City of Lost Souls, a town in Act 4, by speaking with Leda. If you've forgotten how to reach this town, take the Plains of Judgement Portal to get here. This quest is one of the few quests in the game that will give you +2 Skill Points each time you complete it on all 3 difficulties. For this reason it's highly recommended you never skip it.

For this quest all you need to do is find the Deep Caverns in The Far Plains (pictured on my map below) and defeat Krog the Toothless inside. Open the Urn he is guarding and pick up the Ashen Powder then return it to Leda in the Upper City of Lost Souls to complete the quest.