Usually completed after you've reached level 61, or you won't have collected all of the quests required inside. There are five bosses, one of each of the Elements. Once the Guardian of each valley is killed, the player gets a message, "The Guardian of the Valley of is awakened", so players wishing to kill the bosses must kill the Guardians first, and those on kill tasks from a Divine Emissary, etc, can safely ignore them. These bosses are also the target of the Bounty Hunter quests for levels 61-70 and may be offered at 71-80 as well.