Considering the Villa Belvedere in Siena?
A VT member wrote the following comment about visiting Siena:
Bus from/to Firenze by paulileena
Costs 6,50? and takes 1.15 hours to get from Siena to Firenze. Very convienient. Just take a bus from buscentral (near fortezza) with a text Firenze rapido. There is another bus with txt Firenze direta but this bus goes through Poggibonsi and Colle di Val d'Elsa (and is some 20 min slower).
Rapide goes like twice in an hour: 7.10; 8.00; 8.10; 8.50; 9.10; 10.10; 11.10; 11.50 (you will get a time table from the ticket office down below the bus station).
Remember to buy your ticket beforehands and validate it when you step in. You can buy two tickets at the same time (in both directions)