well, since I don't know what your "normal routes are, the best I can suggest is south to 20 trowards Clear Lake. south on 53 to Lower Lake and hwy 29 over Mt St. Helena to Calistoga. then either head out Petrefied forest road toward Santa Rosa keeping left onto Calistoga rd to hwy 12 thru Sonoma and Sears pt. or from Calistoga south on Silverado trail to Napa and 121/12 to
S P. if you can handle rougher roads take Oakville Cross rd from the trail to Oakville grade rd, Dry creek rd, Trinity rd to hwy12 at Glen Ellen, then south.
there is no excaping the flat and booring valley until hwy 20, but hwy 45 along the river does have some turns in it and I find it more injoyable than 5 or 99.