Surrounded by Nob Hill heavyweights (Grace Cathedral, Mark Hopkins, Flood Mansion, et al), Huntington Park vibes light with a children's playground, many dogs, great views, a well-kept garden, fountain ("Fountain of the Tortoises"), etc.
Picnicking is good option when the fog is at bay - be sure to bring a blanket or use the benches (dogs). The California cable car line runs right along the park for those seeking a lift.
The small block for the park was donated by the heirs of Collis Huntington (one of the Big Four railroad tycoons) who also created the much bigger and better known Huntington Library and Garden outside Los Angeles.
Address: Huntington Park, SF