Take a hike! Independence Trail near Nevada City is a dirt wheelchair and stroller accessible trail. Then, a waterfall!
Difficulty: Easy to moderate based on whether you stay on the main trail or head down to the swimming holes.
The trail is well marked so no GPS tracks are necessary, although sites do have several peoples' tracks loaded.
Do be prepared to avoid poison oak! All of the warnings expected such as: don't dive from rocks, kids need life vests, no glass containers, and so on apply.