If you want to go on a fun cruise, a great ship to go on is the Quantum of the Seas which is part of the Royal Caribbean Cruise Line. It's one of the first "smart" ships and has lots of fun activities. You can go skydiving, surfing on water and on the Internet, and eat excessively, without leaving the ship.
My favorite activity was RipCord by iFLY, which is indoor skydiving. You wear a special blue suit, goggles and a helmet. A giant fan blows under you and pushes you all the way up in the air. There is an instructor with you so you are safe. If you spread your arms out you go higher. The ride is on the back of the ship so you can see the view of the ocean when you are flying. The ride lasts one minute. I wanted it to last longer. It was a really weird feeling to fly and a little scary but it was great.
FlowRider is like iFLY, but for surfing. You have to ride on your surfboard without falling off. When you do fall off, the waves push you back to the top. You have a nice view of the ocean from FlowRider.
The wave pools are fun too. There is one inside the ship and one on top. When the ship moves, the motion creates a natural wave. I recommend you try it next time you take a cruise.