If you enjoyed Knight's Castle, here are some other titles you may like:
A Wrinkle in Time
by Madeliene L'Engle
Meg's father has been missing for a year. When she finds out he's slipped through a tesseract, a wrinkle in time, she, Calvin, and Charles Wallace set out to rescue him!
by Christopher Paolini
In Aagaesia, a fifteen-year-old boy of unknown lineage called Eragon finds a mysterious stone that weaves his life into an intricate tapestry of destiny, magic, and power, peopled with dragons, elves, and monsters.