Beltane Ranch is located at 11775 Sonoma Hwy, Glen Ellen, CA (click here for Google Maps).  It's about 6 miles north of Sonoma and will be on your right if you're heading north. 

There is ample on-site parking.

There are four airports that are reasonably close to Glen Ellen.  The following list goes in order of distance (shortest to longest):

        Santa Rosa Airport (22 miles) -- limited routes (see below)
        Oakland Airport  (66 miles)
        San Francisco International Airport (73 miles)
        Sacramento International Airport (82 miles)

For folks traveling from Seattle or Portland, Horizon has several daily flights to Santa Rosa.  San Francisco is the major airport in the area and offers more routes and possibly cheaper fares.