The Large Brass Key is an item featured in The Crystal Trap. Used to open the Iron Door and thus entern the Cavern, the key can be found in three different places: in the Tree Witch's hut, in the Desert, and in the Swamp, all depending on which path Princess Zelda chose at the Stone Pillar Crossroads.
If Zelda goes through the forest, she must choose to climb the rocky path, where she will eventually meet the Tree Witch. Zelda automatically finds the key if she goes through the swamp, but in the desert, Zelda must choose to follow the palace twice, where she will eventually reach an old temple and the altar that holds the key. However, seeing as the Witch's Ring is necessary to obtain the Magnifying Glass, the best path to choose from the forest, desert, and the swamp is the forest, since without the Witch's Ring the Large Brass Key is useless as Zelda cannot free Link without having all three items as dictated by the Fairy's Scroll.
- "The key fits neatly into the lock and with a gentle shove, Zelda pushes the iron doors open. Inside, the road disappears into an immense cavern. The walls glow with an eerie light." (The Crystal Trap (Archway) pg. 32)
- "'I--I have to go,' she says quickly. 'Can you tell me the way out of here?' The witch points down the canyon. 'Follow the creek bed and you'll get where you have to go. Oh, you'd better take this.' She fumbles in her town and dirty rags for a moment and pulls out a large brass key. She offers it to Zelda. 'Sure you don't want some stew?' she asks." (The Crystal Trap (Archway) pg. 61)
- "'It's an altar,' she whispers. 'And there's something on it.' She reaches across the polished stone and touches the object. It's a large brass key." (The Crystal Trap (Archway) pg. 17)
- "Zelda wades into the thick, black ooze. Reaching down, she fishes out a large brass key." (The Crystal Trap (Archway) pg. 113)