Let's further discuss Vault 120. Pic related
It's basically a vault of a grid of 1000x1000 rooms that are complete with all necessities and there are 4 slightly larger than head sized holes on each wall at groin level for you to talk to your neighbors
At the end of every 10 days there is a "shift" where a complex system of gears randomly re positions the rooms. An alarm goes off to warn people of the "shift" so you don't get anything stuck in it.