I know San Gimigano very well, having spent 13 or 14 weeks there at the Hotel La Cisterna during the years 1998-2008 - but always in April/May or October. Even at that time of year it can be coach party hell between mid-morning and late afternoon, which is why I did not suggest it for an August visit. Once, I was there over Christmas, and recall having a coffee in a cafe on Christmas morning: the cafe was open until Mass at noon. There is one tower, part of a museum, that can be climbed. This what you will see if you lean over the guard rail and use a Sigma 10-20mm lens at its widest setting. Try not to be there when the bell at the top of the tower rings the hour at 11 am or noon... If you go in August, I would suggest arriving soon after dawn and leaving mid-morning.