Ah, now I'll have to reread A Tale of Time City.

Sometime about ten or twelve years ago, I sent a fan letter to Diana Wynne Jones, and she wrote back and was really nice. She doesn't travel much these days (I understand her health has been one damn thing after another for the last few years), but she would probably get a huge kick out of reading, say, this post, if you ever got the urge to send it to her.