By Car. (approximately 30-minute drive)
You can rent a car in Siena and drive to the Villa. Please find some car rental companies linked here below.
https://www.rentalcars.com/en/city/it/siena
https://www.europcar.com/en-us
https://www.hertz.it/p/noleggio-auto/italia/siena
You can also have a chauffeur pick you up and drive you to the Villa. Please find some chauffeured car agencies linked here below.
https://www.noltrasport.com/en/hire-car-with-chauffeur-tuscany-siena/