As cfblue said so well, Silverado Trail is a great route to ride. I usually park in Yountville (my hometown!) in the lot of Vintage 1870, a sort of "mall" in town. I head north out of town on the main street, turn right on Yountville Cross Road, until it dead ends, and then turn left on Silverado Trail. I head north to Calistoga and then loop around to Hwy. 29 or turn back down the Trail and take some of the cross roads through the Valley. You can easily do 50 nice miles without realizing it (unless it's one of the hotter days).