If you look for a synthesis of historical Indian culture and almost Italian vacation setting, Mamallapuram is your place. It is one of the most touristic places in Tamil Nadu but you do not feel crowded amomg tourists. The hotels offer fair quality and you can walk out in the evening for a pizza (or Thali) with a beer and a sea view. People are relaxed and there is only few pressure from the shopkeepers to make you buy something.
In addition to this, Mamallapuram (or Mahabalipuram) has stunning historical sights. The probably largest relief in the world (descent of the Ganga), the prototypes of all south Indian temples (five Rathas) and an very old vishnu trivikrama.