The Library Puzzle is the first major puzzle in One Leaves. Found in the school, it involves you moving various bookshelves in order to find a way out of the library, whilst avoiding flying books. As you move shelves, however, the pattern in the room shifts, potentially impeding your progress. The narrator describes it as "a kind of messed-up Rubik's cube".
In the far right corner of the room, you'll discover an Easter egg.