Castiel: It's a doorway to another world.
Dean Winchester: Anoth-- What, like Narnia?
Castiel: No. No, through there it's Earth, but... but different. It's a -- it's an alternate reality.
Sam Winchester: So it's a Bizarro world? Or like the place we got zapped to where we were, uh, uh, actors on a TV show.
Dean Winchester: The supernatural wasn't real. And you were Polish.