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.