With train it takes too long, it is very difficult to make it a day trip from Florence - car is the way to go.
If you don't want to drive, the next best thing is a tour where you go by bus direct from Florence - check the first 3 options on here: https://www.partner.viator.com/en/13...+from+florence
The third one is a private tour, as opposed to the first which is most definitely a large group one (you can tell by the price).
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