We wanted to try zip lining and chose Princeville Ranch Zip N' Dip. There are two others in Kauai, one that only has one zip line that allows children 10 and over and a canopy tour on the south side, but you have to be 15. My 12-year-old really wanted to do it, so we chose the Princeville Ranch's version, which has a minimum age of 12. It was quite an adventure!
You are attached to a cable by a harness and zip across ravines etc. There were a total of eight zips. You start out with one that's probably about 100 feet to get comfortable with it. It's very safe, because the lines are made to hold 3,100 pounds, only one person goes at a time, and you have a backup cable. The weight range is 80 to 270 pounds. You need to weigh enough to zip across. The heavier you are, the faster you go. I never mastered the landings; some zippers could land on their feet, but I usually came in backwards, doing a crash landing. I'm definitely not athletic. It still turned out okay. They just said it was my style. They have slopes so you land safely. The longest zip is 750 feet.
You also go over a swinging bridge two at a time, are harnessed in for that, and can terrorize your partner by making the bridge really shake. Towards the end, you come upon their private swimming hole, complete with a waterfall. After swimming, and, yes, by then you'll definitely want to cool off, you have a picnic lunch, which consisted of self-made deli pita sandwiches, cut-up fruit, and cookies. It's a steep but short climb down, and the hardest part of the excursion was the steep climb back up. Did I mention I wasn't athletic?? If I can do it, just about anyone can.
The whole excursion lasted around 5 hours. It was exhilarating and a highlight of our trip. You can check out the various Kauai zip lines at http://www.trykauai.com/Kauai_Ziplines.htm.