The architecture in the game implies an interesting history, and the fact that is never explained or addressed directly is really compelling to me.

I never finished ICO, but this description makes me think you might really like Hyper Light Drifter! It's got this same kind of deal, a lot of Implied Lore and hints in the environment, without a lot of concrete answers, (and a gorgeous visual style also)

it's rly hard baseline imo but iirc there was an easy mode at least