Yes, it works.Bus take off from Firenze to Siena every day from early morning(since 6), a non-stop bus takes about 1 hour and 20 minutes. There's two bus station around Railway station, check out the one locate at the west side(there's no big sign, if you are not sure, then ask people and they know)Siena is small enough to be explored by feet in 3-4 hours.Book your special ticket to Rome and wish you a good trip.
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