What to do with extra day in Siena

Maybe have a look at where the trains go and see if anything appeals to you.
Trenitalia.it

If you are staying in a hotel, I am sure they will have a ton of Brochures offering tours to other places. We signed up for a Chianti & San Gimignano day tour that was awesome (except for the intense fog that did not let you see the country-side). The hotel called and signed us up for the tour.

Julia,
The bus is a better option out of Siena, see http://www.sienamobilita.it/mappe/Mappa_EXT.pdf

Do you feel that you'll be 'all done' with Siena at that point? I've been several times, and will return many more times, and part of its draw for me is simply being able to walk around the beautiful city. The food, wine - yum, and top-notch. If you want to get out of the city, what do you plan to do the rest of your time in Italy? Did you want to see the Tuscan countryside, go wine tasting, or what exactly on Roberto's tour? That will help narrow the responses you receive.

Hi Julie, I am an American living in Siena. I know it sounds boring but simply "be" ing in Siena is great. Here are my ideas: Wake up at your leisure. Have a stand-up coffee at the nearest bar, and a pastry. If you are a runner, go to the Spanish (Medici) Fort and run around with all the other crazy people. Or, just have a morning walk there. It is elevated (for the occupying Florentines and Spanish to view the town) so it has great views. Wander through the streets, but not the main ones. Go on the back streets so you get a feel for what life was like in 1350, etc. Sit wherever you can (benches are scarce) and just observe all of the fashions and interesting tourists. At 1 pm, go to my friend Moro's restaurant. It is called "Il Capitano" and they speak English. Have a long lunch there, with many courses, talk, relax, eat, drink. You can't do anything in Siena from 1 to 3 anyway because the shops are all closed. If you are not too hungry, share the first course, then share the second course. Their gnocci is to die for, and I love their raw meat (carpaccio?) dish. Just have the house wine, red or white. Tell them Beth and Caracalla sent you, which will help. It always helps to have a connection in Italy. (continued) Beth Young
Siena

(continuation) Then it might be hot so go to the Santa Maria della Scala Museum or the Museo Civico. I just replied to a question about them so you might want to see that query. Time for gelato so just make sure it says "artiginale" (artisinal) on the shopfront for the real stuff. You may want to go back to your hotel and just start happy hour, take a nap, read, whatever, shower. Don't try to eat dinner before 8 pm; it's just not done. Even if the restaurant is open, the full crew is not there and the food may not be great. It's like going to an American restaurant at 4:30. I like Il Pomodoro and one that right off Il Campo on Via del Porrione (leaving Il Campo, look to the left halfway down the block. It is just a menu and steps to walk up. It is BEFORE Osteria le Logge). The food is delish. The owner is my boyfriend's friend but he doesn't know my name so just say Caracalla's friend (l'amica di Caracalla) sent you. Beth Young
Siena

Hi Beth! Just want to say thank you once again for your great suggestions. I really appreciate your wonderful and personal details- we depart for Rome in just a few hours- and look forward to great adventures- Grazie Mille!!

I was going to say hop on the bus and take a nice tour of San Gimignano but then I read Beth's comments above. Now I would want to stay in Siena and follow here suggestions. What a lovely description of what to do in Siena.