I along with a friend drove from Palo Alto to Muir Woods which is located 11 miles from the Golden Gate bridge. The designated parking lot is quite small and we were not able to park there. (We reached there around 10 am) But there is plenty of road side parking if you drive a few minutes pass the parking lot.
Muir Woods has over 6 miles of hiking trails (pay just $1 and get the hiking map - it's very useful if you are not a frequent hiker in Muir Woods). It was one of the best hiking I have ever done - you get to walk along giant red wood trees with voices of nature, the less hiked trails give this clam and peaceful feeling to you. I would definitely go back again there when I get a chance. It is not an exaggeration to say that you sometimes get the Pandora feeling in the Avatar movie.
The temperature was around 60-70 F. I took my jacket with me in case it is cold inside the wood, but I did not have to use it. Make sure you take a bottle of water with you if you plan to do a longer trail - we hiked for about 3 hours - but you need a full day or more to cover all the trails.
Talking about the trails, there is one main trail which is flat and even wheel-chair accessible; most people walk along this - so it is somewhat crowded. Other trails are either longer or with some rough paths and slopes (medium to difficult). They are not hiked by many people and you get to experience a calm and peaceful environment. We hiked along Fern creek trail, Camp East Wood trail and Hill Side trail - all I would say are of easy to medium difficulty. Most of the time we were hiking along a path with a small water stream flowing next to the trail. There are several other longer trails which we did not have time to cover - Lost trail, Ocean view trail, Redwood trail and Coastal view trail are some of them.
If you are visiting the bay area and a nature lover, I would definitely recommend this place.