San Francisco Bay Area
One of our favorite places to hike in Oakland is at Redwood Regional Park. It is packed full of trails that take you along streams and through the hills among lush redwood & oak forest that are covered with beautiful ferns. Even on a busy weekend the park and trails never feel crowded since there is such an abundance of trails and picnic areas. This is the place to be when the weather is HOT! Once down in the canyons you are shaded by the giant redwoods giving you at least a 10 degree drop in temperature. One of the best features of the park is the sheer size and amenities. You can pack a lunch and spend the entire day hiking or come after work for a short 1-2 hr hike.
We discovered this park several years ago when living in Walnut Creek. It is a quick 20min drive once on the freeway through the tunnel. During summer we would go after work arriving sometimes around 6pm and hiking until 7:30-8pm since the sun is up longer.