The Battle for the Castle by Elizabeth Winthrop

In the sequel to The Castle in the Attic, Mrs. Phillips’s gift of another magic token enables William and Jason to travel to Sir Simon’s medieval kingdom, where they must battle an invasion of giant rats and resolve their own troubled friendship.

The Indian in the Cupboard by Lynne Reid Banks

A boy receives a box that turns his toy figures into living, tiny, humans, and he must learn to treat them kindly and help them find their way to the worlds where they really belong. It’s a story about respecting people of different cultures and learning to cooperate. The book won five awards, generated four sequels, and was adapted for the screen.

The Book of Three by Lloyd Alexander

During the Middle Ages, a boy joins forces with a powerful knight to battle an evil wizard, but the knight disappears, and the boy teams up with a spunky and magical princess, a goofball troubadour, and an oracular pig to complete the quest. The first of the five-novel Chronicles of Prydain series, its lessons about responsibility, courage, and loyalty help make it a widely admired and influential book in the fantasy genre for young readers. Alongside its sequel, The Black Cauldron, it was loosely adapted as a Disney animated feature film.

Yvain, or the Knight with the Lion by Chrétien de Troyes

Written in the late 1100s by the writer who invented Sir Lancelot, this epic poem recounts the adventures of Yvain, a member of King Arthur’s Knights of the Round Table. He wins the love of a wondrous princess, neglects and loses her, and must undertake several dangerous tasks—saving a lion from a dragon, freeing a castle from an evil giant, and rescuing the princess’s lady-in-waiting from a deadly conspiracy, among other feats—before he can mend the damage between himself and his true love. The tale is packed with references to the ideals of chivalry that overtook European literature during the High Middle Ages. As such, it’s source material for fantasy stories like The Castle in the Attic.