The Yountville AVA.

Guide books often refer to the town of Yountville as being the "culinary capital" of the Napa Valley.  Indeed, famed chef Thomas Keller has three acclaimed restaurants, and a stellar bakery (yum), in this small town.  However, Yountville, to me at least, is more significant as the place where grapevines were first cultivated in the Napa Valley.  Oh, and Yountville also has great Christmas lights.
George Calvert Yount was the first United States citizen to be awarded a fairly sizeable Spanish land grant from the Mexican government back in 1836.  Yount called his land Rancho Caymus and on it he built a cabin and a grist mill making him the first Euro-American settler in the valley.  In 1855 Yount paid for a surveyor to lay out the boundaries for a village he called Sebastopol, despite the fact that there was a nearby town, one valley over, already named that.  Eventually, in 1876, two years after Yount's death, the town was renamed Yountville in honour of it's founder.
Yountville did not become an American Viticultural Area (AVA) until 1999.  With 2,700 acres of planted vineyards, this AVA has a rather unique climate.  Moderated by the Yountville Mounts (which is actually just one rather large hill that waylays the marine fog as it advances up, through the valley), the relatively cool climatic conditions here lend themselves to great grape growing.  Interestingly, there are more grape-growers than actual wineries in Yountville.  For example, Gamble Family Vineyards is considered an Oakville winery, but they produce a Yountville AVA Sauvignon blanc, that I have enjoyed in the past, which hails from a vineyard in the AVA that they own and farm.  I have, however, also enjoyed wines from wineries that are in the Yountville AVA proper, e.g. Goosecross Cellars, Dominus Estate and Noah Vineyards, to name but a few.  Yountville is a compelling AVA.
Four down, twelve to go.