Minecraft wiki entry for Island_survival, associated text: Underwater Ruins are another rare structure that has the potential to greatly benefit a player's survival game. They generate mostly underwater, although if you are lucky enough to find one that generated on land, you effectively have a half-done house. As an added bonus, underwater ruins also contain chests with loot and treasure. If you have access to a conduit, you could use an underwater ruin as a base. Beware, however, as underwater ruins may potentially be inhabited by drowned which can, in the worst-case scenario, spawn with tridents, granting them a lethal ranged attack. Drowned are extremely dangerous underwater because they have no distraction from a limited breath meter.