Napa Valley is not like it used to be. It's become a victim of its own success. 8^<
There are several wineries in the valley that are more than 100 years old. In the last few years, they keep building more 100-year-old wineries! Every time I go up there there are another half a dozen 100-year-old wineries that have been built since the last time. They are all very picturesque!
My favorites used to be Inglenook and Beringer. They are both in the town of St. Helena, which is really the center of Napa Valley. The visitor's center at Beringer is a beautiful house built by the Beringer Bros. in the 1880s with beautiful oak carvings inside and stained-glass windows that are centuries old. It's worth the tour just to see the house. Beringer ages their wines in caves dug into the side of the mountain, and that's pretty cool. On a hot day it's like walking into a refrigerator. Inglenook is also built around a beautiful old house that belonged to the founder, Capt. Niebaum.
Mondavi and Charles Krug are the other -genuine- 100-year-old wineries.
In 'downtown' St Helena is a huge stone building that used to be Christian Brothers' winery, but now is the Culinary Institute of America. You can go inside, there are exhibits and things in there.
Just keep in mind that there are two roads that go through the valley north/south. One is Hwy 29. EVERYTHING is along this road, every winery, every town, every overpriced restaurant and specialty hotel, and on weekends stop-and-go traffic. The other road is the Silverado Trail, a nice, relaxing drive through the vineyards, a view of what the valley looked like before it became a tourist mecca.