If you like "Knight's Castle"...
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.
Knights of the Kitchen Table
by Jon Scieszka
When Joe receives a magic book for his birthday present, he, Fred and Sam are transported to a time when evil knights, fire-breathing dragons and vile-smelling giants roamed the land.
Over Sea, Under Stone
by Susan Cooper
Three children and their Great-Uncle Merryman search for the grail in the caves and cliffs of Cornwall. Part of the Dark is Rising series.