The fictional world entered through the wardrobe in C.S. Lewis’s novel is Narnia.
Lucy Pevensie reaches Narnia by walking through a wardrobe in The Lion, the Witch and the Wardrobe, published in 1950. Narnia is a separate fantasy world populated by humans, talking animals, fauns, dwarfs, giants, and other creatures. It is ruled or protected by Aslan, the great lion who serves as its central spiritual and moral figure.
The wardrobe is not the only route to Narnia. Across the seven books, characters also reach the world through magic rings, paintings, a railway accident, and other unusual crossings. The setting includes locations such as Cair Paravel, Lantern Waste, and the eastern sea.
Narnia is sometimes mixed up with Middle-earth, Neverland, or Earthsea. Middle-earth belongs to J.R.R. Tolkien, Neverland to J.M. Barrie, and Earthsea to Ursula K. Le Guin. Narnia is specifically Lewis’s creation and gives its name to the entire fantasy setting.