The Wood between the Worlds was an actual wood in "The Magician's Nephew". It had pools between the trees which were the portals to different worlds. Digby compared the wood to the attics of the row of terraced houses he and Polly lived in. I believe that Lewis was experimenting with different metaphysical transportation concepts when he wrote this book which was the first one he wrote, considerably before "The Lion, The Witch and the Wardrobe". Note the use of the yellow rings as another means of getting from Earth to Charn; he was a friend of Tolkien's at the time that Tolkien was writing "Lord of the Rings" and could easily have decided to use the same device. I believe that he read from "The Magician's Nephew" at the meetings of the informal literary society that Tolkien, Lewis and several others formed in Oxford.

Although I haven't read the book for twenty years or so, I do remember the sinister verse associated with the bell which Digory rings to waken Jadis:

"Heed thee well, impetuous stranger.
Strike the bell and bide the danger
Or wonder till it drives you mad
What would have followed if you had."

I could have some of the words wrong, but I've remembered this since I was ten years old or so, so it clearly made an impression!

"The Magician's Nephew" was completely different in its approach to the rest of the "Narnia" series (as TEd will be finding out anew, reading them with his kids). In some ways it was almost not part of the series; rather a precursor, exploratory novel in much the same way that "The Hobbit" was to "Lord of the Rings".

I much enjoyed these books as a kid, and when I read the series again, back to back, some twenty years ago I found that I enjoyed them quite as much again on one level, but I also realised that the good/evil dichotomy was perhaps too pronounced for adults to swallow whole.