Napa is a valley rather than a town, and a session here is planned around which end of it you are in. Downtown Napa, Yountville, St Helena and Calistoga are spread across thirty miles, and the character changes as you go north — flatter and more agricultural at the south end, narrower and more wooded toward Calistoga.
The thing that catches people is that the vineyards are working farms, not scenery. They are private property, almost without exception, and photographing in one requires the winery’s permission. Most wineries with an events programme will arrange it and most charge a site fee; pulling over on the Silverado Trail and walking into the vines is trespassing on a crop.
The second thing is the calendar. Harvest — "crush" — runs from roughly mid-August into October, and during it the wineries are working at full capacity. Access for photography narrows sharply, and the vines that turn gold and red in the photographs everyone wants do so in late October and November, after the fruit is picked.