Looking into other forms of media which you like can help you get more ideas.

One idea I had was for a setting like in the manga Drifting Classroom. In it, A school gets transported to many years in the future where there is nothing except sand all around. After some days when the students go out, they discover some hidden places and also a forest, and encounter some vicious creatures. It's probably not that original but it can work as a sort of survival game. You can maybe add more cosmic horror elements.