Kajak na moru! Sea kayaking in Dubrovnik is a must-do. It's a wonderful opportunity to build upper arm strength, spend time with loved ones, circumnavigate a medieval walled city and an island, all from the pleasure of a plastic, floating armchair. A wee bit of effort is involved, but mainly it's a 4-hour lark well worth the €35 - 50 (depending which company you use). We went with Adventure Dalmatia, headquartered in Dubrovnik's tiny West Harbor in Pile Bay (aka "Kings Landing" by GoT nuts). The scenery was exhilarating, lunch was a surprisingly tasty sandwich in tinfoil and we stopped for a swim in Betina Cave before paddling back. Worth every Kuna!

More info: http://adventuredalmatia.com/one-day-activities/sea-kayaking-dubrovnik