The most southern area of Napa is Carneros.  Carneros the ideal location for growing Pinot Noir and Chardonnay grapes but you will find other wines at the wineries as well.  This is a tour that offers tremendous flexibility as the tour includes mostly wineries that are open without appointment.  Although Carneros can get busy on the weekends it is far South of the heavier traffic areas of Napa so it can be an excellent choice on a busy Saturday or Sunday in Napa.