The Usborne Puzzle Adventures:

It's an ordinary day for Hallie and Martha... until they accidentally wake two knights from a thousand-year sleep and find themselves on a daring and dangerous quest. Flung back in time, they must travel through the ancient kingdom of Hamalot in search of Good King Stan. For only Good King Stan can save both the past and the present from the evil threat of the mysterious Dark Dark Knight. Full of coded messages plus logic, map and maze puzzles to unravel as you read, this Usborne classic has been updated and enhanced for a whole new generation of puzzle adventurers.