Library Key

The is a quest item found in  that serves to open Eyeglass Island Library.

Location and Uses
After curing King Zora's deathly illness with the Magic Potion in the past, the king gives Link the Library key in the present. King Zora hopes that Link can research the cause of the filthy seawater at the Eyeglass Library, which has left Lord Jabu-Jabu near death.

Upon entering the library, Link discovers that, long ago, Fairy Powder was kept in the back of the library, but it had since been taken away. In the back of the library, Link finds an Old Man who gives Link the Book of Seals. Link returns to the library in the past and gets the Fairy Powder from the back of the library. To get to the Fairy Powder, Link must solve a puzzle using the Book of Seals from the present.

With the Fairy Powder, Link lifts the curse on the Queen Fairy, who will then cleanse the seas. This allows Link to enter Jabu-Jabu's Belly, the seventh dungeon of the game.