Subnautica is an underwater open world adventure game. Craft equipment, pilot submarines, and out-smart wildlife to explore lush coral reefs, volcanoes, and cave systems. Subnautica is an underwater open world adventure game. Craft equipment, pilot submarines, and out-smart wildlife to explore lush coral reefs, volcanoes, and cave systems. Full details on the latest status of the game, how you can give feedback and report issues can be found at http://playsubnautica.com.