Very scenic State Park. The hike up to the top of Bald Mountain is quite strenuous, but you're rewarded at the top with spectacular views from San Francisco to the snow-capped Sierra.

If you can time your visit so that you can attend a star party at the observatory in the park, you'll have a great opportunity to totally nerd out for a few hours. We were able to see the Crab Nebula and Jupiter (and several of its moons) through the telescopes.