At Arakas Druid Camp, find an NPC called Lantalir Rainmist.
Talk to him and he will mention that he is searching for a Book of Feylor located at the Ruined City.
To reach the Ruined City you must pass through the Labyrinth.
But before you begin your trip, be sure to have an Iron Key in your backpack.
Go through the Labyrinth and find the exit to the Ruined City.
Search for a locked chest (located NW from the entrance).
Your iron key will open the chest and you will find the Book of Feylor.
Go back to Lantalir Rainmist and say Book of Feylor to him.
Gain :
Note: You can do this quest as many times as you want.