I've played 3, NV and 4 but it was all quite some time ago. I just started replaying 4 and for some reason I can remember parts of a specific vault storyline but can't remember exactly which game it might have been from, never mind which vault.
There's also a chance I'm misremember some or all of the details (or completely dreamt this up and it doesn't actually exist).
Basically the vault is inhabited by a faction that initially appear friendly but it turns when the lone wanderer realises they're not who they say they are and they're raiders or similar.
I also seem to remember it having something to make the interior appear more pleasant to live in than it actually is, when it's actually really run down. Like some kind of projected images or similar. Something involving a projector. Also a large farming area with crops.
Have I completely made this up in my head? Am I misremembering and taken parts from different vaults? Ant help would be appreciated, I've been reading through the accessible vaults from the three games and none of them seem to fit the bill.