If you're downtown, go down the Embarcadero to Rincon Park! This landmark has nice groomed patches of grass along its promenade and there is a large sculpture of a Bow and Arrow known as "Cupid's Span"; in addition, the view of the Bay Bridge is unforgettable and worthy of a photo!
Rincon Park is owned by the San Francisco Recreation and Park Department.
J/K/L/M to Embarcadero Station; N or T to The Embarcadero and Folsom.
30X-Marina Express to Howard and Spear; walk down Howard towards the waterfront, the park will be to the right.