Subnautica 2

Subnautica 2 is an underwater survival adventure on an all-new alien world from Unknown Worlds Entertainment, the next chapter in the Subnautica universe. Driven from your home by ongoing conflict, you accept Alterra’s offer of a new life, but the colony ship CICADA, which is carrying you and your fellow Pioneers to your new home, goes awry. The ship’s AI insists the mission continue, and you are stranded and have to survive. The game is in Early Access.

You explore vibrant biomes in the Tadpole submersible, design and customise bases to return to when the depths become too dangerous, and craft tools. Long-forgotten ruins are scattered across the ocean-covered planet. There are four pre-designed characters, and as Early Access develops more tools, equipment, vehicles and customisation options will be added.

According to HowLongToBeat, the main run takes about 14 hours and a full run about 30, but these are player estimates for the Early Access version, so the figures may change with updates. In a month at roughly 60 hours you have more than enough time. The developers describe it as a single-player experience that can optionally be played in online co-op with up to four players in total.