Which fictional location is featured in the children's novel published fourth in "The Chronicles of Narnia" series by C. S. Lewis?
Underland
Title: The Chronicles of Narnia: The Silver Chair
Passage: The Chronicles of Narnia: The Silver Chair is an upcoming fantasy adventure film based on "The Silver Chair", the fourth novel published in C. S. Lewis's epic fantasy series "The Chronicles of Narnia" (and sixth in internal chronological order).  It is intended to be the fourth installment in "The Chronicles of Narnia" film series, and the first film in the series to be produced by C. S. Lewis Company.  This will be the first film in the series to be distributed by TriStar Pictures and Entertainment One and the first not to have the involvement of Walden Media.  The film's release date has yet to be announced.
Title: Underland (Narnia)
Passage: 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.
Title: The Silver Chair
Passage: The Silver Chair is a high fantasy novel for children by C. S. Lewis, published by Geoffrey Bles in 1953.  It was the fourth published of seven novels in "The Chronicles of Narnia" (1950–1956); it is volume six in recent editions, which are sequenced according to Narnian history.  Like the others, it was illustrated by Pauline Baynes and her work has been retained in many later editions.
Underland (Narnia) The Silver Chair