Russian Hill Open Space is right behind Russian Hill Park. It's not accessible to explore (it is partially surrounded by a tall chain-link fence and partially by apartment buildings and condos); however it adds to the ambiance and green-ness of the neighborhood.
Russian Hill Open Space is owned by the San Francisco Public Utilities Commission.
Additional Info
Wildlife sanctuary not open to the public - PUC/Clean Water Program
Muni access:
19-Polk -- Francisco St. and Polk St.; walk east (uphill) on Francisco St. to Larkin St.
30-Stockton or 47-Van Ness -- North Point St. and Hyde St.; walk south two blocks (it's a bit uphill) just past Francisco St.
Powell-Hyde Cable Car - Hyde St. and Bay St., south on Bay (it's uphill) to Francisco St.