“The Wood between the Worlds”

I may be looking at this too simplistically, but if I recall correctly from my own childhood reading of the Narnia books, the passage between the two worlds was a wardrobe: one opened the front door, pushed through the clothes, and came to the back of the wardrobe, which was the door to Narnia. So, what is the back of a wardrobe made of? Wood, of course: “the wood between the worlds.”

Just a guess as to an alternative meaning –