One of the most popular medieval hill-towns of Tuscany is San Gimignano. I've read that in summer it's a real tourist zoo, but at around Christmas (when we were there, hence the Christmas lights) it was nearly deserted and full of ancient atmosphere. Like many of the Tuscan hill-towns, it never quite recovered from the Black Death of 1348, so much of the place is truly medieval, not much rebuilt over the centuries since. (That structure in the middle of the square is the top of a medieval cistern, from 1273 but still functioning, from which the square gets its name.)