Your spaceship crashed onto an alien ocean, and you have to figure out a way to not only repair or rebuild it, but also survive in the meantime.
Subnautica is an open-seas singleplayer survival game introducing gamers to an environment hardly ever seen in gaming, let alone on such scale and this the survival genre. Swim through sun-lit surface waters admiring colourful wildlife, build a base to find a respite from endless water and prepare to venture into the dark unfriendly depths.
Subnautica does an excellent job at simulating underwater adventures and exploration.