Valakas is slumbering in the dungeon beneath the Forget of Gods. To prevent him form avakening, you need to go to Valakas' Temple and explore it. Your party must have 15-100 warriors of Lv. 76 or higher. Weaker heroes won't be able to complete the mission. The raid lasts for 60 min., and every Wednesday the zone is reset, so you can only go there once a week.