Royal Caribbean has outfitted some of its bigger ships with a zip line. The zip line is quite high: 9 decks high to be precise. It’s also about 80 feet long. It’s not the same as zip line for real where you have multiple legs, but as close as you’ll get on a cruise ship! You have to remember to have laced shoes with socks and your clothes can’t be wet. You can read the detailed account here.
Royal Caribbean has outfitted some of its bigger ships with simulated surfing machines. We used the FlowRider on the Oasis of the Seas (there are two aboard, one for surfing and the other for boogie boarding) and it was a lot of fun. It’s not the same as surfing for real, but as close as you’ll get on dry land (or a ship)! We’d never done this before so it was tricky. The water moves at 35 to 40 miles per hour. The surface under the water is a little bit padded, but there is a real chance of injury if you fall. You can read the detailed account here.