I have not a favorite place for picnic, maybe because since I was a child I use to walk in the forests close to home to search mushrooms with my parents and we use to take a break to eat (usually bread and salama or something similar ^_^). I would to have a romantic picnic with Paolo, but before I have to persuade him to walk in the forest for a bit :D
Tell him about the great food and bottle of wine you have planned for him if he goes with you on a forest picnic. That should do the trick :-)