If there ever was a place to get a good hour exercise in, Lafayette Reservoir Trails rank in the top ten of the San Francisco Bay Area. Anyone can walk this paved trail which is 2.7 miles circling the reservoir.
Shaded by many trees, and usually a calming breeze, the trail is full of nature with deer, birds, squirrels, fish, wildcats, and much much more. Although I have never seen a mountain lion, I may have caught a glimpse of a bobcat once.
In addition to the paved trail, there are several fire trails circling the reservoir. But these are "quite" hilly and should only be attempted if you are in good health and physically fit. It can get very dry and desolate on the fire trails. Other hikers/people are rare. Always hike in pairs or groups.