Minecraft wiki entry for Adventure_survival, associated text: If you prefer to explore the ocean, shipwrecks and buried treasures (for those you'll need to remove the sand covering the chest with creepers) are the only structures which can be looted, as you cannot dig the blocks covering the chests in ruins, making that structure useless, another structure that is useless is ocean monuments which provide nothing more than just a challenge due to you being unable to break sponge and gold, nor use prismarine from guardians as you cannot place blocks made from the prismarine you crafted.