A great day trip is Muir Woods to see the redwoods. You take to ferry to Sausilito, then get on a tour bus. It's a scenic 1-1.5 hour drive each way. You have about two hours to hike or just walk around. NEVER go on the weekend. There's only one road in/out and it can back up for miles. Buy tickets in advance at the counter near Pier 39.