How would you build a realistic fantasy world if you were given unlimited time and unlimited resources?

Ok so let's just say that say hypothetically you are given unlimited time and unlimited resources. (Like I don't know, a computer that can do anything you want, an infinite number of people helping you, a million lifetimes to finish, infinite money, etc etc. So we can just throw those out the window and focus solely on methods.) How would you go about building a realistic fantasy world?<br><br>like from the geography to the languages, all the events in history, the cultures of the different races etc etc. How would you go about building all of that?<br><br>What I've been doing is just thinking about it in my head for years while occasionally writing stuff down but I have a feeling that isn't the most efficient way to do it.