The fantasy world in C.S. Lewis's Narnia books is called Narnia.
Narnia is both the name of the wider fictional world and the kingdom at the center of many of the stories. Its history begins with creation in The Magician's Nephew and continues through successive ages involving humans, talking animals, dwarfs, giants, and other creatures.
The world includes places such as Cair Paravel, Lantern Waste, and the underworld reached in The Silver Chair. Earth and Narnia are connected through magical portals, including the wardrobe, rings, and a railway accident in The Last Battle.
Narnia is often compared with other fantasy settings, but it is not Middle-earth, the world created by J.R.R. Tolkien. Lewis and Tolkien were colleagues and friends in Oxford, which sometimes leads readers to blend details from their separate fictional universes.