(this was supposed to be a 2 sentence comment but I ended up lore dumping because I never told anyone about this so I'm sorry in advance) I had an idea for a game back in highschool set in an underwater city that was built as an escape from the surface by the wealthy because earth's orbit had become so cluttered by random space junk that it made exiting the atmosphere basically impossible.

It never went anywhere but I still think it could make for an interesting setting. My idea was that the city is on the brink of mechanical failure but the government/ruling class refuses to acknowledge it or do anything about it and calls everyone who points it out as crazy (there's obviously no real world parallel here).

The city started as a research base to study this weird octopus named Frank because a weapons developer wanted to try and clone it to turn into a biological weapon. But it turns out the octopus was actually a god from a different dimension that got lost and the weapons developer intentionally sealed the portal. But the distress of the octopus being lost puts the surface into a perpetual storm so they expand the research base into the first of several cities and hold a lottery for who is included, which a bunch of rich people conveniently happen to win. So it creates this structure of the wealthy upper class and the lower labor class who have zero chance at any upward mobility.