"Uh." Damn, really shouldn't have opened his big mouth, should he? "It's complicated. The wardens say people 'get lost in the dimensional stabiliser' but no-one really knows what that means."
He pauses, studying the Doctor. Should he elaborate? The Doctor, of anyone, deserves to know the little they've found out about this place, but he doesn't want to overload him within minutes of his arrival. On the other hand, this is the Doctor. Pretty impossible to overwhelm.
"You should know something, Doctor. This place - this whole dome--" spreading his hands to incorporate as much of it as he can "--isn't real. It's virtual, all in our heads, and we're all actually lying in pods somewhere, dreaming this."