Which C.S. Lewis book begins with children discovering a magical wardrobe?

The C.S. Lewis book that begins with children discovering a magical wardrobe is The Lion, the Witch and the Wardrobe.

Published in 1950, it introduces the Pevensie children—Peter, Susan, Edmund, and Lucy—and their journey from wartime England into Narnia. Lucy is the first to enter the other world through a wardrobe in a room of the country house where the children are staying.

The book features the White Witch, the lion Aslan, and a Narnia trapped in a long winter. Its combination of adventure, fairy-tale motifs, Christian symbolism, and child protagonists made it the most familiar entry point for generations of readers.

The title is sometimes shortened informally to The Lion, the Witch and the Wardrobe, but the title includes the final noun exactly as printed. The book was the first Narnia novel published, though some editions place it second in internal chronological order.