Which C.S. Lewis book begins with children entering a fantasy world through a wardrobe?

The C.S. Lewis book in which children enter a fantasy world through a wardrobe is The Lion, the Witch and the Wardrobe. It was published in 1950 and became the first published volume of The Chronicles of Narnia.

The story follows Peter, Susan, Edmund, and Lucy Pevensie, who discover the land of Narnia inside a wardrobe. Narnia is trapped in an endless winter under the rule of the White Witch. Lucy is the first sibling to enter, and the others later follow her into the new world.

The title is sometimes confused with other Narnia books because the series has several recurring characters and locations. Prince Caspian begins with the children returning to Narnia, while The Silver Chair follows a different quest. The wardrobe itself is central to this book, not merely a decorative detail.

Lewis wrote seven Narnia novels. The series has appeared in stage, television, radio, and film adaptations, but the original book remains the source of the wardrobe adventure.