She's quite serious, of course, and is about to tell him as much when he does start to exhibit the kind of amazed curiosity she wholly approves of. Much like the Doctor, she is particularly fond of this moment, showing off to someone new; it's been repeated uncountable times, but no two introductions are alike. The fact that Aziraphale probably should be less astounded than the average human, by virtue of his age and experience, only makes his reaction that much more satisfying. And a bit charming, really. There's so much she could show him.

Now she does smile, and nods to his request. "Be my guest." Quite literally, though it would be better if this was happening in the waking world. For one, she could learn more about him that way too. Following him inside, she anticipates the usual questions that occur at this point. "I am dimensionally transcendental - my interior is virtually infinite. The exterior was once a disguise, but I grew so fond of it that I kept it on."