The Key of Thundera is one of the pieces of the Treasure of Thundera. While not possessing any magical powers by itself, the Key is the only item that can unlock the Book of Omens.

Any being that enters the Book of Omens is ordered by the Guardian of the Book of Omens to present the Key of Thundera. Failure to do so results in the intruder being showered with flames by the two giant dragon heads beside the guardian.