Open your world map and look under the quests tab. There should be a quest list and that one should be in there as well. It tells you where to start the quest and at what level you can start it. You can start portions of it I think at lvl 74 by doing two of the side quests early. If you haven't started the alliance with Orcs or Silenos yet, you might want to get started on it as this does take a while to do to get to alliance level 2. There is also a quest in Hot Springs that you need to complete as well.