The SFMOMA, or San Francisco Museum of Modern Art, has all kids of interesting, mostly weird (to me at least) paintings, photos, sculptures, even video-based art pieces. I went there a few years ago for my high school art class. All kinds of events take place here, like exhibitions, film screenings, lectures, etc. I personally don't have an eye for what's good art and what's not, but modern art is still visually stimulating nonetheless. My favorite exhibits are the Frank Lloyd Wright pieces, because I'm an architectural enthusiast.