Most have heard of and even read "The Lion, The Witch, and Wardrobe" by CS Lewis. There are 6 other books in the series. At the end of the series "The Last Battle" Lewis contrast the "new Narnia" with the "old Narnia." He writes:

It is hard to explain how this sunlit land was different from the old Narnia, as it would be to tell you how the fruits of that country taste. Perhaps you will get some idea of it, if you think like this. You may have been in a room in which there was a window that looked out on a lovely bay of the sea or a green valley that wound away among mountains. And in the wall of that room opposite to the window there may have been a looking glass. And as you turned away from the window, you suddenly caught sight of that sea or that valley, all over again, in the looking glass. And the sea in the mirror, or the valley in the mirror, were in one sense just the same as the real ones: yet at the same time they were somehow different deeper, more wonderful, more like places in a story: in a story you have never heard, but very much want to know. The difference between the old Narnia and the new Narnia was like that. The new one was a deeper country: every rock and flower and blade of grass looked as if it meant more. I can't describe it any better than that: if you ever get there, you will know what I mean.