Muir Woods is one of my favorite places to go. This link has some helpful information for first-time visitors: http://www.nps.gov/muwo/planyourvisit/index.htm

There are hikes with different lengths (http://www.nps.gov/muwo/planyourvisi...d-vicinity.htm --the map here doesn't show the different hikes as clearly, but I remember that when I went to the park, they had maps that clearly showed which trails were the 30min hikes and which were the longer ones)

If you would like to do a hike but would prefer to stay closer, may I recommend the San Francisco Land's End hike? The trees aren't as impressive, but the path goes along the bay, and there are portions where you can walk down to the water. There's also a labyrinth that's pretty cool, and a large rock that you can climb for a great view that is right next to the labyrinth. Parking isn't a problem at either end of the trail, although I usually park in the Sutro Baths parking lot (not sure if that's the official name, but the lot is at the Sutro Baths end of the trail rather than the Legion of Honor end.)

Labyrinth:
https://localwiki.org/sf/Land%27s_End_Labyrinth

Land's End info:
http://www.nps.gov/goga/planyourvisit/landsend.htm
http://parksconservancy.org/visit/pa...lands-end.html