I was thinking of doing an RP which takes place right after the sun goes out. It would start off normal, but night all the time, and everything would get gradually colder. People would gather around geothermal shifts, and dig underground to avoid the cold, and would become like a really cold Fallout Vault simulator. Some time later, you manage to make technology to go to tunnel other underground cities, or be able to brave the cold surface. Not sure if this is the best summary, but what are thoughts about this?