My first guess is The Legend of the Golden Snail by Graeme Base (https://www.goodreads.com/review/show/118071373), but the locked cubes don't match with my memory, and it might not be quite old enough.

Second guess is that it is one of the Usborne puzzle adventure stories (https://en.wikipedia.org/wiki/Usborne_Puzzle_Adventure_series or https://www.librarything.com/series/Usborne+Puzzle+Adventures will give you titles), but I don't know enough about them to make a guess.