Since Montmartre has a cool Metro station, it's good place to talk about public transportation. I managed to navigate entirely on foot and by train for the week (including to/from the airport). It's very easy to use and the Bonjour RATP app is great for figuring out schedules and routes. I also need to thank my high school German teacher, Frau Lee, who spent an evening preparing a bunch of high school kids from central Wisconsin who maybe took a bus occasionally for navigating public transportation in European, and Rolinka for adding to that knowledge that you need to know either the last stop in the direction you are going OR the last stop in the direction you are not going, which definitely made things easier.