Minecraft wiki entry for Island_survival, associated text: Finding a buried treasure chest on the island can be a boon for survival, because the chest often contains treasure such like iron and gold ingots, various types of fish, (in rare cases) iron swords and leather tunics ‌[Java Edition only], cake, TNT, potion of water breathing or regeneration, and chain armor‌[Bedrock Edition only]. Buried treasure chests are also guaranteed to contain a single heart of the sea item, which is used alongside 8 nautilus shells to craft a conduit. Nautilus shells are drops from the drowned, which are underwater zombie variants. They can also be caught as treasure from fishing. Buried Treasure is much rarer than shipwrecks and are also much harder to find, as they consist of only one block. However, if you find one (and are able to craft the conduit), you need to find some prismarine, dark prismarine, prismarine bricks or sea lanterns (all of which are found in ocean monuments), and you could construct yourself a conduit and live underwater.