If you think that cruising only means days at sea with a dash through various ports-of-call, stop right there. Some of the world's great cities—Barcelona, Miami, Singapore—are where you'll start and end your time on board. So why not fly in a little early to get some quality time on land? It means you'll have to unpack more than once on your cruise holiday (sorry!) but it's totally worth it. Below, how to do five of our favorite ports in a day.