Decided to check out the CA Academy of Sciences nearly a year after it's opened. My wife is a school teacher so we got in for free (normally $25/person). It's located in the middle of Golden Gate Park. I'm not science geek, but I was quite fascinated with the experience. I wish they had these museums when I was growing up. My favorite exhibits were the fish tanks, the Rain Forests, and the albino alligator.
They have a whole section about global warming and the impact on animals and the environment. They really try to send you a message about living a "green life" by telling you drive less, stop buying bottled water, and many other stuff we do in our daily life.
It's a great way to spend the day. You should set aside a good 4 hours to get the full experience (and get your full $25's worth). You can hang out at the park afterwards.