San Gimignano, Volterra and Siena in one day?

I think your plans are very aggressive.

First, all of your driving times are at least a little under ViaMichelin's estimates, which people often say are optimistic. It's usually suggested that drivers pad those times. Check especially the time from Siena to Venice, which VM puts at over four hours, not three.

Second, you'll need time to find a place to park the car and then walk to the historic area for sightseeing. If you haven't already done so, Google for parking information so you can figure out how far away you'll have to leave the car.

Third, if you're planning to have a restaurant meal in Volterra, it might chew up a large part of the two hours you've planned there. If you're just going to grab take-out food, I guess it might work.

Fourth, Siena is normally proposed as a full-day destination if not longer.

Finally, you're planning to park the car twice on the Florence-Siena day (and possibly in Modena on the next day) with all your travel possessions in it. Theft from cars in touristy areas is a significant problem. There's some risk even with everything hidden away in the trunk. Be sure to carry expensive/hard-to-replace items with you during your sightseeing jaunts, and don't open the trunk to put things in it after parking.

Aside from the question of whether you can say you "saw" a major attraction like San Gimignano in 90 minutes (Siena is about 10 times bigger than that), you have totally unrealistic ideas of the "overhead" involved at each stop. Aside from the confusion of avoiding the dreaded ZTLs, most of these places have parking some distance from the town center, with long uphill walks (or, at best, a half-hourly bus). Then you have lines to buy tickets to see the interior of the churches and other sights. (Perhaps you were only planning to glance at the exteriors before running on to the next landmark?) Do you know you'll have to settle for a stale pre-made sandwich for lunch? You have no time to sit down for an Italian meal .... Did you hear that the food is very good it Italy? The idea of parking more than once to see Siena in high season is ... .... crazy.

Despite your precision planning, you have left out the month of the year in your post. That is crucial in Tuscany, because of the massive crowding of the area in high season. You also have to take into consideration how tiring it is to tour in sweltering heat. One lane roads can have delays at the drop of a hat.

Too much, drop Volterra. Even then too much. As mentioned you are short changing the overhead. Example: dropping the car in Venice sounds easy but it is cumbersome. Parking in Siena is a ways from the city center and you have to walk around the sights, San Gimignano can be a parking nightmare and usually is. Driving between Volterra and San Gimignano is slow and the country side is picturesque, take your time. There is a lot to experience in any one of these cities and each deserves the time.

I have driven from San Gimignano to Venice with kids in tow. Four hours sounds about right after you add in lunch (Autogrill) and potty stops. We took the rest of the day to see some of Venice in the evening but the kids were dead on their feet.

My advice, slow down a little and enjoy what Italy throws at you.

Hi Scully, We have been to all three and I would skip San G. We stopped there on a RS Tour and it is an interesting sight from a distance with all of the towers, but both Volterra and Siena have a lot more to offer. I would drive straight to Volterra in the morning and see as much as you want then spend the rest of the day in Siena. The Roman ruins and the Etruscan Museum in Volterra are definitely worth a visit. We visited Volterra on a trip we took on our own so had a rental car. There is a huge parking lot below town and you have to walk up. We spent two nights in Siena with the RS Tour and wish we had stayed longer. The Cathedral and Museum are wonderful and the climb to the stop of the tower on the main piazza had beautiful views overlooking the city and countryside. Whatever you decide, I'm sure you will enjoy it!
Teri

I think your kids would enjoy Volterra much more than San Gim. Tons of things for them to do.

Do think you need to increase your projected drive times.
Florence-Volterra about 90 minutes. Volterra-your Castel about the same. From there to Siena around 40 minutes.

The back roads of Tuscany are
A lot of fun to travel, lots of hills and blind curves. Biggest hindrance we have found are lots of bikers and motorcycles.
Scenery is beautiful.

Last year in February we toured Siena , San G, Pisa back to Florence in a day. It was too much. 12 hours. San G is a nice very small town which we liked but not enough to give it more time over other choices this next trip.
But here is a more important reason to cut your itinerary back, a lot; This area I assume is new to you. That means the unfamiliar and you will need more time to find your way than you are allowing. It just isn't a fly by place with the way towns are set up and entrances you will have to locate. I was on a tour where it was done for me and I would not do the itinerary as written above. The cathedral in Siena has some great things for your teenagers that should go over well, time to explore. The Cathedral has a crypt area below that is significant, the gate of heaven is an area at the ceiling level that walks you past views of the interior from above and outside for views from the top of Siena and surrounding countryside, and I haven't said a thing about the dozens of different pope's heads statues lining all across the upper area all around the interior. The marble floor holds one story after another depicted in marble that takes some time. It takes at least an hour for the shortest walk through, two plus if you see the crypt and gate of heaven area. Then there is the tower climb down by Campo Fiore. The line for that I here goes fast but does take time. Siena is a day long place.
I hope you will cut way back and give those in your party the opportunity to see, filter and absorb what they see and relax in a place that they will never forget, hopefully for very good memories. Plan like you will come back as there is just too much to see and it just can't be rushed. The place isn't built for that.

This one site in Siena can take up 2.5 hours or more> Siena Cathedral http://operaduomo.siena.it/en/sites/

You can visit both San Gimignano and Volterra easily in one day, and I would because they are both worth a visit, but I wouldn't rush to Siena to get there by 5pm. You can walk around a bit Piazza Del Campo and maybe dine around there, in the evening, but you should leave the visit of the Palazzo Pubblico (with Torre Del Mangia and museo civico inside) and Duomo/Baptistery to the next day. Those are the must do in Siena and if you start early you can do everything by lunch time. Have a late lunch then drive to Venice. Give yourself at least 4 hours, because you will have to stop to refuel before returning the car and find your way to Piazzale Roma across the bridge (Ponte della Libertà) from Mestre. I think the rental offices close late there, certainly not before 7:30pm. Leave Ferrari for another trip.

Thanks so much for all the helpful input. I can't tell you how much I appreciate it. I was thinking about how we did it with our guide last year. Pop in here, out there, etc. I wasn't taking into account him knowing the area so well, and dropping us off so that we didn't need to deal with parking.

I was using Google Maps, putting in the time of day we'd be leaving, where it gives real-time driving estimates based on what traffic is normally like at that time of day. I hadn't heard of the other site. Thanks for those tips.

My new plan is to just go to Volterra, and explore for several hours, and stop for lunch at a lovely place before heading to Siena. We'll check into our hotel, which has free parking on site since it's outside of the city walls, and drop off our bags before we head back into Siena to explore in late afternoon/early evening and have dinner. I do like the idea of returning to Siena the next morning before driving to Venice. I think you're right, Ferrari is one stop too many on the way to Venice. I do have a lovely friend who lives in Bologna, so perhaps we will stop there for lunch and meet up with her before continuing on to Venice.

Just do some Google Map street tours to see how Volterra and San Gimignano compare. Siena is far too big and interesting to squeeze in as an after thought. At night when the tour groups are gone it is magical for shopping and eating. You will only be disappointed that you have rush there, and during the day it can be very crowded with tourists. If you are lucky enough to be there during a market it will be very memorable. Just say no to 3 and even 2 cities in one day.