I am taking a night train out of Florence to Nice. I leave at 11:30 pm from Campo di Marte. So my question is 1. Where exactly is Campo di Marte, I can't find much about it? and 2. If it's not within walking distance, how do I get there at night, do buses run there at that time?
Go to www.viamichelin.com. If you enter Italy as the country, Campo di Marte as the station, and Firenze as the city, you'll get a detailed, zoomable map. You'll see that Campo di Marte is just north of the Arno River. It's about 3km east of the Santa Maria Novella station. If it's too far to walk and buses don't run late enough for you, take a taxi.