If you look closely, there is no book more visual than Three Trapped Tigers, in that it is filled with blank pages, dark pages, it has stars made of words, the famous magical cube made of numbers, and there is even a page which is a mirror.
“People always tell me I'm nothing like my character. Well, hopefully not! He's a character who's very defined. He was purposefully written by Jo Rowling as very one-dimensional in the first few books, because you're supposed to hate him.”