At this undeveloped state park 8 miles north of Calistoga, the long-extinct volcanic cone of Mt St Helena marks Napa Valley’s end. It's a strenuous 5-mile climb to the peak’s 4343ft summit, but what a view – 200 miles on a clear winter’s day. Check conditions before setting out; it often gets snow in winter. Also consider 2.2-mile one-way Table Rock Trail (go south from the summit trailhead parking area) for drop-dead valley views. No dogs allowed.
Temperatures are best in wildflower season, March to May; fall is prettiest, when the vineyards change colors. The park also includes the old Silverado Mine site where Stevenson and his wife honeymooned in 1880.