If you want to try for a single-city cultural victory, do you need to decide this at the beginning of the game? How late can you make this decision and still have a chance? I've ever won this way or even tried to, but I might if I could decide on it in the Middle Ages, instead of starting a game saying "this is a 20k game." I like to be flexible in my strategy. (The article on this site implies that you do have to begin the game with this type of win in mind.)