First, you have to get lvl 45 and go zone into Maidens Gulch. This mini zone is located at the top of Lavastorm at the end of a deep trench. In this zone, you will find the sage of ages, who is under attack by some nasty drakotas. These are groupx2 mobs so you'll need 11 other people with you to take them down. Once you rescue the sage of ages, he gives you a quest to go deep into Solusek's eye and speak with Naggy. Before you go down to talk to Naggy, make sure you speak giant.
I really don't want to give away any more spoilers. This quest is probablly the most fun quest I have ever done in any game, and this is enough info to get you started. The reward is the title, "of the shard" and your prismatic weapon.