Well, you only have to invest your time, of course. I found there are many adult fitness playgrounds in public parks around where I live. Rengstorff Park in Mountain View has some gym type equipment, for example a chest press or an exercise bike. If you are feeling young and spirited you might even consider the skate park near the pool. Or the tennis and racquetball courts. In fact, the park is so large that a pick up soccer or basketball game would be possible, even on crowded days.
The exercise options of Sylvan Park, also in Mountain View, and of the Hillview Community Center (Los Altos) are more old school.
With places in both to do sit-ups and pull-ups, here your choice would be which location you prefer and which material. While in Los Altos the bars are blue and steel, in Sylvan Park they went with wood.
Do you have a favorite outdoor gym?