Any idea for a romantic date in miami?

Hi, Im 18 and so is my boyfriend, we are lets say a pretty boring cuople. We dont like parties or clubs we are most of the quiet type. Im usually very creative but I'm running out of ideas. I want a nice palce that the two of us can be alone and have like a picnic or so. I've been trying to find like a cave or waterfall near miami but not very successful in the search. I just want somehting very romantic not a restaurant or anything common.. any help will be gladly considered =)