Rent a two-person kayak in Cavtat and paddle along the beautiful coast. The great thing about kayaking is that it's not only so much fun but also a good workout. You will need upper body strength and balance to operate it.
That being said, the best feeling is knowing you are doing it all by yourself! You will be able to catch sight of the beautiful sea and incredible nature all around Cavtat. Plus, the staff provide the safety equipment and instructions, so you don't have to worry about anything.