On past trips to San Francisco and Northern California, I had never really thought about going to see the redwoods in Muir Woods... after all, how impressive could a bunch of trees be? Nonetheless, I had several friends (and my mom) recommend the place to me... and as I was on my way to surf a spot in Marin County, I happened to drive past a sign pointing to Muir Woods. I made a mental note of the location and on my way back from surfing, decided to check it out. I was really impressed (wish I had brought my good camera with me... all of these are Galaxy SII images). The trees are so massive that they almost look "cartoon-like" in stature. In many cases, the leaves or branches don't even start until about 100 feet up and many of the trees have been here for over 1000 years. Apparently, the redwoods in this forest are considered to be "coastal redwoods" (which are smaller in size)... the really big redwoods are further north by the Oregon border.
If you have a bit of time while in San Francisco, I recommend taking the short drive over the bridge to see the Muir Woods. There are also a bunch of shuttle buses that will take you from the city.