Big Key

Big Keys are large key items that appear in The Legend of Zelda: A Link to the Past, The Legend of Zelda: Four Swords Adventures, and The Legend of Zelda: A Link Between Worlds. Big Keys are similar to Boss Keys as they are required to open a boss door, but Big Keys can also open large Treasure Chests.

In A Link Between Worlds, they are instead found within large treasure chests, making them even more similar to Boss Keys.