Siena: Leaving the car outside the city is a good idea. There are some park sites where you can leave it and from them the center is in walking distance.
You will eventually end up in one of the most beautiful squares in Italy, the famous Piazza del Campo, where the Palio (the horse race) takes place twice a year- 2 July and 16 August if you are interested- Watch this presentation by Andrew, who was so lucky to see it this summer, that you can also check in his youtube channel.
At the Piazza del Campo make sure you don't miss the Gaia fountain -actually a 19th century copy f the original one from the 15th century by Jacopo della Quercia- and the Loggia della Mercanzia before you give your whole attention to the imposing city hall, il Palazzo Pubblico -built from 1297 to 1342- and its tower, La Torre del Mangia -1348. You may want to go up, it seems the views are amazing, though I can not tell by myself as my fear of heights proved itself stronger than usual. When I was there I was told that the tower -102 m high- has this name due to its first bellringer, known as "mangiaguadagni" (literally "the one eating profits" because he was very lazy. The wikipedia gives a slightly different version.
|Palazzo Pubblico and Torre del Mangia|
And you can not leave Siena without visiting its cathedral and its museum, by now you will have probably been seeing it all day among the roofs.
Monteriggioni. After Siena make sure you don't miss a visit to this charming walled town on the top of a hill, impossible to get lost as you will spot it from far away on the road! You may find interesting that Dante used Monteriggioni as a symbol in the Divina Commedia. Monteriggioni celebrates a medieval festa in July. Have any of you been there? I would like to read some opinions on it.
Watch this wonderful pictures presentation by Giorgio to see what it's like