The drive is about 2-3 hours from San Francisco via the Golden Gate Bridge, Marin, Napa Valley, and a steep and windy climb over Mount St. Helena, which separates Napa and Lake counties. The trick to making it a fun and relaxed drive on a busy weekend day is to leave the city early enough to get through Marin before traffic gets bad, which is usually around 11am or so. Once you turn off 101 in Novato, it is a beautiful drive through the Carneros wine region to 29 in Napa.
In Napa we always get off 29 and drive east a few miles to hook up with the Silverado Trail. This is a much prettier and less congested drive than 29, which tends to get really busy in Napa Valley on weekends. On the Silverado trail you are also less likely to encounter half-drunk winetasting tourists trying to control their rental SUVs and Mustangs.
It takes about 45 minutes to drive from Napa to Calistoga on the Silverado trail and in Calistoga you rejoin 29 going into the mountains. This drive over Mt. St. Helena is one of the steepest we frequently take with the bus, but aside from impatient rednecks in pickup trucks and SUVs there is little trouble getting the bus safely over the mountain. I have no temp gauges (or anything except a fuel gauge), so no idea whether the bus got hot (it was in the 90s), but it felt fine. The views are beautiful and I hear there is an excellent hike at the top, but we have never done this.
Once you are over the top of Mount St. Helena it is an easy downhill cruise into Lake County. You reach Middletown in about 20 minutes. There is a good brewpub in town, a last chance for a beer before Harbin Hot Springs, which does not allow alcohol.
Harbin Hot Springs is about 15 minutes northeast of Middletown (go to www.harbin.org for precise details). You pay $30 per person for a 24-hour visit and that includes camping or sleeping under the stars on one of their outdoor decks. Aside from the pools (hot, warm, and ice cold, all featuring water from natural hot springs some of which are heated by volcanic activity), there are lots of other activities, including a theatre where you sit on pillows and where they show excellent movies, great hiking opportunities, a good restaurant, yoga, massages, etc. The pools are open 24 hours a day, year round.
Below is a picture of our campsite at Harbin. We didn't take many pictures because the clothing optional aspect of the resort means that they don't encourage picture taking. They also don't encourage bringing small children and don't allow pets, so it takes some organizing if you have a dog. We go here at least 4-5 times a year and would go more often if we could find the time. It is one of the most relaxing places to escape to from the SF bay area and the fact that it is such a wonderful drive through the wine country makes it even more worthwhile. Our bus is the ideal camping vehicle for trips like these.
Be careful what kind of tree you park under: this woke us up in the middle of the night. It sounded like the whole tree came down on the poptop roof.
By the way, I kept track of where I got gas (no working odometer) and calculated fuel consumption of 16.8mpg. Not great, but not bad given the steep and windy roads.
