Get out of town for the weekend! Drive north past Napa and Sonoma, past Mendocino, into the little town of Fort Bragg (actually bigger than Mendocino), and visit Glass Beach.
Glass Beach was originally a city dump, but the tides have turned the glass dumped there into the world's largest collection of sea glass. Over the years, unfortunately, selfish tourists have carried away a lot of the glass as souvenirs, but there's still quite a bit there.
After you've spent a few minutes checking out the glass, spend some time observing Glass Beach's true beauty - her tide pools. You can find urchins, sea anemone, and all kinds of kelp and seaweed growing in the shallow tide pools at Glass Beach.