Really? Silent treatment? It's not the worst Dean has been presented with, and after decades of silence, it's really not the most effective way to get to him. Still, it reminds him of how young his captive must really be. Alone, trapped with a monster, exchanging his freedom for his father's when he doesn't even know who what his dad did.

So Dean sighs, tries his best not to sound gruff when he turns to start walking, sure
this time that Castiel will at least follow. "Um...You're welcome to the castle, you know, if you get bored of the room. There's...art on the walls." And he frowns inwardly at himself, "Oh, there's a library."