Scenery, thats what i'd call it.
There are lots of buildings etc we cannot access there.
The fact we see it, would make it not so secret.
The fact that folks think its significant, is imagination (and a bit of hypothesis)
Nothing wrong with imagination unless you try to force it as reality.
Not having any actual facts, makes it hard to hypothesize its purpose (other than scenery).
Whats the empty room in Port Royal for?
Whats the room full O barrels in KH for?
Shhhh its a secret.