Subnautica is an open-world survival game set in an alien ocean planet called Planet 4546B. Players control a character who survives a spaceship crash and must explore the underwater environment to gather resources, craft equipment, and build bases. The game features a variety of marine life, both friendly and hostile, and players must manage their health, hunger, and oxygen levels while navigating the depths. The game emphasizes exploration and discovery, with players uncovering the mysteries of the planet through various biomes, such as coral reefs and deep-sea trenches. Subnautica also includes a storyline that reveals the history of the planet and the fate of previous inhabitants, enhancing the immersive experience.