Start Hardmode by defeating the Wall of Flesh at the lowest part of the map after you summon it by destroying a Guide Voodoo Doll by throwing it into the lava in The Underworld. The five chests are Jungle , Corruption , Crimson , Hallowed , and Frozen. Each chest has its own key. Kill mobs in their respective biomes to have a rare chance for one of the keys to drop. After you have the key and have found the chest, kill the Plantera Boss in the Jungle biome. Note: To kill Plantera, you must first kill all three Mechanical Bosses.