day trip to siena, italy

(Siena, Italy).  We were excited to take a day trip to Siena.  We didn't know much about the city other than that it was a medieval city built atop a hill.  I was told that the Duomo* in Siena was one of the most beautiful in Italy and also, that they have horse races in the Piazza del Campo* during the Palio.  We missed the race (which had just happened a few days before our arrival), but I'm guessing it would have been a madhouse.