The Chronicles of Narina by C.S. Lewis

Second Hand 

The Lion, the Witch and the Wardrobe tells the story of four adventurous children: Peter, Susan, Edmund, and Lucy Pevensie, who have been evacuated to the English countryside in 1940 following the outbreak of World War II. They discover a wardrobe in Professor Digory Kirke's house that leads to the magical land of Narnia.
Narnia is a charming, once peaceful land inhabited by talking beasts, dwarfs, fauns, and giants. Unfortunately, it has been frozen in eternal winter and enslaved by the power of the White Witch. The arrival of the children, with the return of the Great Lion Aslan , gives Narnia hope for liberation . . . but with a great sacrifice.