Enter the Kromise Caves and use the Explo Powder SGL that was given to you by Areth. The item is only usable around the 4th giant spawn point inside the cave ( -95, -24, -1097 ) /waypoint -95.49, -23.79, -1097.39. You have to be standing in exactly the right spot.
When you use the item, four monsters each conning 49vv will spawn and attack you. They do not need to be killed for the quest.