The Magician's Nephew by C.S. Lewis

The Magician's Nephew by C.S. Lewis is a delightful story that highlights the beginnings of all the comings and goings between Narnia and Earth, in particular how the wardrobe in Professor Kirk's house became a magical portal to begin with. In the story, young Diggory Kirk and Polly Plummer make friends and decide to go exploring in the shared crawl space above the attic rooms in the houses where they live. (They live in a long row of houses, and the crawl space evidently goes all the way from one end to the other.) Trying to get into the abandoned house for some exploration that is just beyond Diggory's house, they make a mistake and end up in the attic room of his house. By bad luck, Diggory's mad uncle is there, and tricks Polly into picking up a magical ring that transports her to some other dimension. This of course, forces Diggory to go after her to rescue her. (His uncle is not decent enough to go after her himself.) And this begins the two friends' adventures wherein they meet the evil queen Jadis, and the noble lion Aslan. And will Aslan be willing to help Diggory find something in Aslan's new and growing world of Narnia that will cure Diggory's terminally ill mother? Read the book and find out! The Magician's Nephew was first written in 1954.