Matthew Lew has a list of 21 private parks for the public located in San Francisco. He calls them POPOS and many are located on building rooftops and in between city buildings. They may not necessarily show up as a public park on Google Maps which is why Matthew has gone out of his way to visit so many of them and document their existence. And best of all, they don't have to be a secret! Visit one, or all of them, in your San Francisco neighborhood!