House of Many Ways by Diana Wynne Jones
House of Many Ways follows Charmain, a bookwormish girl whose sheltered upbringing is her downfall when she’s forced to house sit for a wizard uncle she doesn’t even know.
Charmain is unprepared for the house itself. But she is prepared for reading–and that makes her indispensable to the Wizard Howl, in this sequel to Howl’s Moving Castle.
She stood with her nose up, sniffing delightedly. It was the delicious mildew fragrance of old books.