Key Cavern is the third Dungeon in The Legend of Zelda: Link’s Awakening. To reach it you need the sword, shield, the shovel (which you can buy or steal in the shop) and the Slime Key, which you can get by collecting all 5 golden leaves. The Key Cavern dungeon is located east of Mabe Village in the Ukuku Prairie.
Key Cavern Map
Key Cavern Bosses
Throw bombs in front of their mouths and they will eat them. After they ate one they will run around with their mouths shut so wait until they open their mouths again.
Use the Pegasus Boots to run against a wall to make Slime Eye drop. Hit his eye and use the Pegasus Boots to split it into two. Finish each eye to defeat the boss.