The fictional land visited by the Pevensie children in C.S. Lewis's fantasy series is Narnia.
Narnia is the central setting of The Chronicles of Narnia, a seven-book series published between 1950 and 1956. The books follow children from England who enter a parallel world where talking animals, mythical creatures, kings, queens, and magical events shape the story. Different books reveal different periods in Narnia's long history.
The Pevensie siblings—Peter, Susan, Edmund, and Lucy—first reach Narnia through a wardrobe in The Lion, the Witch and the Wardrobe. The series later introduces other human visitors, including Eustace Scrubb, Jill Pole, and Digory Kirke. The recurring figure Aslan is the great lion associated with Narnia's creation and protection.
Narnia is sometimes confused with Middle-earth, the setting of J.R.R. Tolkien's works. Tolkien and Lewis were friends, but they created separate fictional worlds.