Which C.S. Lewis book features a wardrobe as a portal?

The C.S. Lewis book featuring a wardrobe as a portal is The Lion, the Witch and the Wardrobe.

Published in 1950, the novel follows Peter, Susan, Edmund, and Lucy Pevensie after Lucy discovers an entrance to Narnia inside a wardrobe. The children become involved in a conflict between Aslan and the White Witch.

The wardrobe is one of the most recognizable gateways in children’s fantasy literature. Lewis drew on ideas of imaginative transformation and traditional Christian symbolism, although he did not write the series as a simple one-to-one allegory.

The book is often called the first Narnia story because it was the first published. In the series’ internal chronology, however, The Magician’s Nephew describes events that occur earlier.