Task: Explanation
Input (English): The Underland is a fictional location in the children's fantasy series "The Chronicles of Narnia" by C. S. Lewis. Described by Lewis as lying beneath the land of Narnia, Underland appears mainly in The Silver Chair, where Eustace Scrubb and Jill Pole travel under the ground to reach it in their search for Prince Rilian. They find him in Underland and release him from his enchantment by The Lady of the Green Kirtle. Question: Which fictional location is featured in the children's novel published fourth in "The Chronicles of Narnia" series by C. S. Lewis? Answer: Underland
Output (English):  Described by Lewis as lying beneath the land of Narnia, Underland appears mainly in The Silver Chair, where Eustace Scrubb and Jill Pole travel under the ground to reach it in their search for Prince Rilian.