Scattered across the centre of San Francisco are almost seventy semi-secret spaces, privately owned but open to the public. Subject to the fine print of a little-known pact between City and Commerce, these so-called POPOS (Privately Owned Public Open Spaces) allow alluring vistas of San Francisco and access to its intimate interiors. However, they are often poorly indicated – perhaps a deliberate tactic by the private companies who own the spaces to prevent the pesky public from using them. Accessing POPOS sometimes even requires walking past security guards, or through unmarked doors. No wonder many are underfrequented.
via Doc Pop