Lo-Fi Games

I stumbled across this freaking term during my translation and got confused. I confused both dictionaries in use and also confused google by asking about self-containment in several forms. I believe it's the description of an Outpost PRISON building, but wtf does that means? Does this thing folds inside like some architectural turtle, or does its internal volume equals external volume, so it's so big it can contain itself?

Text goes as: "A very large, self-containable citadel"

Pliss esplane i inglesh vary bad nid halp pliz

I guess "self-containable" in this context means, "the building is equipped enough to produce sufficient electricity, water, food, cloth, weapon etc. for its dweller." or self-sustainable.
Something like Vault-tec Vault in Fallout.
If containment all by itself does no harm to its dweller, the building can be called "self-containable"

Nice guess, but i don't think any outpost, even s-VI, does that, so i'm still curious