User blog comment:Hdutt2/Hdutt2's BioShock: Downfall-Novel: Prologue and Note by the Author/@comment-6024608-20131006075620/@comment-6024608-20131006114947

Various posting about sequels mentioned :  Space stations/Moonbase (50s era SpaceRace/Cold War  context) and Antarctica (conspiracy stories talk of a secret post WW2 Nazi base there)

Post Apocalyptic has been overdone, but a storyline of some survivors 'sliding' to a better place might work -- maybe a 'vacant' earth where other 'survivors' built a city after doing the same 'sliding' - with twisty stuff of it turning out to be rather bad place (the city 'survivors' brought the same problems that cause their apocalypse in the first place, etc...)

An empty Columbia -- after one too many Tears to steal stuff brought back a plague  or some very mad aliens/people who 'punished' the thieves.