Stinson Beach is about a 30 minute drive from downtown Mill Valley. Take a walk on the beach, and grab a bite at the Parkside Cafe or Sand Dollar restaurant for lunch. Marin Transit buses go to and from Mill Valley and Stinson Beach. Or hike there via the Dipsea Trail (~7 miles each way).
Head to wine country! Sonoma is only about 45 minutes away, or keep going to Napa Valley. Both have endless wineries to choose from. Some of our favorites are Gloria Ferrer, Buena Vista, Hall, and Frog's Leap.