Cooler days on Italy's Amalfi Coast mean more exploring, less queueing. September in Iceland is not quite so disconcertingly 24-hour sunshine-y, and there's a good chance you'll catch a glimpse of the Northern Lights. Barcelona is built for city lovers – it's at its best once the crowds have gone but the good weather remains. If the two of you want to tango, Buenos Aires is in mild mode rather than sizzling-steak summertime hot.