### Instruction:
What should I do on a free afternoon in San Francisco?

### Response:
You can visit and take photos at San Francisco's landmarks such as Pier 39 or Golden Gate Bridge. If you enjoy walking outdoors, there are several large parks in the city. You can visit Golden Gate Park and the various attractions and museums located in the park. The Presidio is also a popular park where you can get some of the best views of Golden Gate Bridge.