Leave from the Ferry Building in San Francisco on a ferry for Vallejo. Then take an electric train to Calistoga and walk a block to your hotel to relax for a week in the hot springs. Those were the days.
Though the tracks from St. Helena to Calistoga are gone, the tracks from Napa to St. Helena still exist and are used by the Napa Valley Wine Train. There is also a bike path that goes on the old right of way from Calistoga south towards St. Helena.
When in Calistoga, be sure to visit the Sharpsteen Museum.
Also check out Indian Springs and Dr. Wilkinson's, both in Calistoga.