I've included three titles below that I hope you might enjoy.
The Secret of Platform 13 by Eva Ibbotson.
Odge Gribble, a young hag, accompanies an old wizard, a gentle fey, and a giant ogre on their mission through a magical tunnel from their Island to London to rescue their King and Queen's son who had been stolen as an infant.
A Wrinkle in Time by Madeline L'Engle.
Meg Murry and her friends become involved with unearthly strangers and a search for Meg's father, who has disappeared while engaged in secret work for the government.