Golden Gate Park is the environmental center of San Francisco, California
. It is located in the Sunset
area of SF on what used to be an enormous sand dune. In fact the ENTIRE Sunset section of SF used to be a dune but they managed to get grass and trees to grow on it. Pretty cool!
Anyway. There is a TON of cool stuff to do in the park. It is located right next to the SF MUNI N train so it is pretty easy to reach.
It is about 1/2 mile wide and 3 miles long and stretches all the way to the ocean. There are a number of really fun things to do. I would recommend the Japanese Tea Garden, Asian Art Museum and the Botanical Gardens. The Tech Musuem is pretty cool too...
After that more 'touristy' destinations, there are a ton of outdoor activities you should turn your attention to. Basically if you start in the Inner Sunset and walk/bike down to the Ocean you will get the full effect. (You should take your time though)
I Mountain Bike in the park about twice a week and it is always fun. The fact that it is RIGHT in the city and so close to the ocean REALLY make this a special place!