I remember with the Prospero book, the scene that was in my mind forever was one of Rachel talking to the Elf on a balcony. I ran this scene over a million times. Since the book took me years to write, I remember the astonishment I felt when I finally reached it and actually had to write it.
With both the Rachel and the Victoria books, there are scenes like that, too. With both of them, they always seem to be scenes many books in. But in both cases, I have the notes from the original game, so I'm not sure I need to write more until I get closer.