The information in this article is from the fan game AGDI universe and is therefore not canon.
Treasure Island is an island between Llewdor and Daventry.
Treasure Island was also a hidden book in the Classic Fiction section of Caldaur's library. A certain number of books had to be pressed in sequence to reveal it. The Child's Key was used to unlock the lock binding its cover shut. On the last page was a map of the castle and the surrounding area which pointed the way to the tiara's location. "A date of fate can be found with a first, a second, and a double of nothing" was written near the bottom.
Behind the scenes
This book is based off of Treasure Island by Robert Louis Stevenson. I is about Jim Hawkins meeting up with a pirate named Long John Silver.