A bit in the History department:
(1) Golden Gate Bridge / Fort Point. Bona fide Civil War era fort, built at the mouth of the San Francisco Bay, at a time when it was feared that there would be Civil War activity there. Park in the lot at the south end (San Francisco end) of the Bridge (good luck finding a parking place), and it’s right there.
(2) Next, drive across the bridge. Notice the mountain immediately at the north end of the bridge, on the right. Take the first off-ramp after the bridge (just after the touristy vista point), and drive up that mountain. (It’s called Fort Cronkhite.) FABULOUS views over the bay, the bridge, and S. F. – clear weather permitting – almost like a view from an airplane. Along this road are several ruins of WW II era fortifications, including an abandoned artillery emplacement at the top.
This puts you into Marin County, so you are already on your way towards Muir Woods. For a good scenic drive, find your way back to Highway 1 and drive up the coast for a while, say, to the mouth of the Russian River. Turn inland there, and drive on that road, through redwoods, all the way to Santa Rosa or any town in that area.
This takes you through redwood forest, including the town of Guerneville. There are some beaches there along the Russian River. There is also a side road there, leading to Armstrong Woods, a redwoods park where you can picnic or hike, with trails of varying difficulty.
From Santa Rosa, there is a somewhat back-country road leading through the hills to Calistoga. (I trust you will have maps or GPS or whatever to find all these roads.) Half-way along that, there is another nearby side-road that passes by a genuine petrified forest. There is a private piece of land there where you can pay a few bucks and go in and take a brief hike through the petrified logs laying all around.
In Calistoga (you’re at the northern end of Napa Valley now), you can poke around. It’s a kinda picturesque but touristy little town. Being at the foot of an old volcano with hot springs, it’s famous for spa resorts – they are in just about every block. Get yourself a good full-body massage. If you’re there as a couple, you could get the full treatment – couples massage, mud bath, facials, the works, if one is into that.
Ask for directions to the Golden Haven spa, which is a bit off the main drag. Ask if Betina is still there!
Then, take Highway 29 south, back toward San Francisco. This runs through the heart of Napa Valley, so you can stop in every little town and tour the wineries. (Although back in Sonoma County, where you were earlier in the day, there are plenty of excellent wineries too.)
That should keep you busy for a day. You’ll see PLENTY of Pacific Ocean, redwoods, and other goodies on this day trip.