The Elen'lu Isles - Act 2 Story Quest
The Elen'lu Isles is the third Story Quest of Act 2 and begins after you complete Finala and the Broken Bridge and reach Elen'lu Isles. You'll find the Elen'lu Isles by going north of where you talked to Finala and following the path through the Northern Vai'lutra Forest. Just before the Elen'lu Isles you'll find a Teleporter which is marked "Elen'lu Isles" in the list of locations to teleport to. This is worth mentioning because in the future when you need to return to the Northern Vai'lutra Forest you'll need to pick Elen'lu Isles in the list.
Once you make it to the Elen'lu Isles you'll want to make sure you activate all of the bridges that you come across by clicking the top of the archway at their entrance (pictured below).
Aside from activating every bridge you come across, all you need to do is explore the Elen'lu Isles and defeat each elite Taclak you find nearby the light refractor and then place the crystal in the refractor that it drops. Once you've done this turn the refractor to face the center of the Elen'lu Isles.
You'll need to turn all 4 light refractors to face the center of Elen'lu Isles (once you turn them to face the center you can't turn them again so it isn't hard to mess up). Once you have activated all 4 light refractors and are pointing them in the right direction you'll want to head over to the main island and fight the elite Taclak here for the Large Prism Crystal. Place it in the Pyramid on this island for a scene after which you'll be attacked by many enemies.
Once you've finished this quest return to Aman'lu and speak with Finala at the southern bridge which will now be fixed. This quest will complete and you'll begin the next Story Quest, The Royal Caravan. Finala will also offer to join your party at this point, she's a Combat Mage with a fiesty personality.