Climb waterfalls or pyramids. See the birthplace of civilization or listen to steel drum bands. Follow the footsteps of history or the wake of a water-skiing boat. A cruise is the easiest way to see and explore new places. On a cruise, you sample a number of destinations that you may want to return to for another vacation . . .
Most ships even have casinos.
Or you can stroll on deck in the evening moonlight. There are also many special events like the Captain's Cocktail Party, masquerade parades, passenger talent nights, etc. The night can go on as long as you want. On a cruise vacation, the entertainment is on the house. There's no cover, no minimum, and no charge for admission.