Book of Mudora

The Book of Mudora appears in A Link to the Past, and is a collection of ancient Hylian lore and stories, as well as a guide to translating the ancient Hylian Language that appears throughout the land of Hyrule. It is found in a library south of Kakariko Village, and is used to allow Link to enter the Desert Palace (the second dungeon in the Light World) and also to obtain two of the three Spell Medallions. There is also text in front of the Master Sword's pedestal which Link is able to read using the book.

Trivia

 * Mudora (also known as Medora) comes from the ancient Greek language, which means "holder of knowledge", "tutor" or "holder of high wisdom", and the Book of Mudora indeed is "a holder of knowledge" that teaches Link the ability to translate the ancient Hylian language.
 * In official artwork, the cover of the book carries a number of unidentified symbols.