If I had to guess, It would look like a castle on the outside, but on the inside it would be a confusing mess of other places and locations with the shadows taking forms to correspond to their areas, sometimes glitching between one form to another as they cross the boundries, or as ghosts wrapped in chains. The cognition would probably be people trapped in crystal or something. My shadow wouldn't be the ruler of the messed up castle, but their bodyguard since I don't like the spotlight. My treasure would be an ID card. Proof that I exist other than in my own mind.
Ooooh. Edgy. Yeah, shut up,