Sandwiched between two fields of grapes along scenic route 12 between Glenn Ellen and Sonoma you will find what their webmasters accurately term "a tranquil, beautiful place like none other" also known as Quarryhill Botanical Gardens.
This facility is on the American Horticultural Society's list of Reciprocal Admissions Program gardens which means that members of the AHS or of any of the RAP gardens can enter free of charge. As members of Concord's Markham Arboreatum my travel companion and I did just that. Quarryhill members can enter free too, of course, but their dual membership costs $75/year and as Retired/Dual members of Markham our membership costs only $30 for the two of us.
Be aware that the pathways in this setting are not paved, and they are hilly, but for those who reserve ahead and don't mind paying a nominal fee, they have an hour long cart tour that goes all through the facility. I walked and was glad I wore shoes appropriate for walking on gravel, but I soon wished I had brought a walking stick. I sure will do that next time, and there will be a next time, soon I hope.