Last week I bought a book of "Japanese puzzles", a rather broad term which, at least over here in The Netherlands, seems to generally apply to so-called nonograms. Series of numbers tell you how many squares in each row or column need to be filled in, but you have to figure out which ones. Usually they have a title which points to the picture that will appear when you finish it correctly.
What I didn't realise was that the book I bought had four-star puzzles, a bit more difficult than I was used to, at least on paper. Fortunately I had found a re-fillable pencil on the train a couple of weeks before, so the time I didn't spend on the train reading this last week, I spent puzzling.
At one point a conductor even made a remark about it. He pulled a folded copy of his own book from his belt (I don't think they have to wear it, but as an addition to their uniform many of them seem to wear this pouch which bears close - too close for comfort - resemblance to a fanny pack. Fortunately it's black or a dark navy, I can't remember, rather than fluorescent.)
I realised there was a website that I used to do these things online, but it seems to have disappeared. But I found another one, that provides random nonograms ranging in size from 5x5 to 25x25 squares. No pictures, but fun. Especially the smaller ones remind me a bit of playing Minesweeper. The larger puzzles are more logically challenging.