How's it possible? "This is Cardiff," Alice says, like that explains everything. She should probably explain a bit further, though. "Apparently there's some sort of space-time rift here, and it sometimes lets things through, or pulls them through, something like that. I don't know very much about how it works."
Very much out of time, and apparently place, to go asking what planet. It's a very unusual situation for Alice, but she can't just walk away now. "What's your name?"