Just outside the city of Gisborne in New Zealand is an amazing water ride that is not connected to any kind of theme park. It is purely a result of the natural flow of the Wharekopae River, and it is completely free to ride.
The Rere Rockslide, off Wharekopae Road, is a flat slab of rock nearly 200 feet long (60 meters) that descends at a 30-degree slope into a deep pool. Water running over the rock has smoothed it over the centuries, making it safe to ride down the slide on some kind of floating device (or, though it is not advised, on your stomach).
All manner of thing is ridden down the rockslide, including strips of cardboard, boogie boards, tires, inflatable mattresses, inflatable chairs, yoga mats, kiddy pools, and inner tubes. They each provide a different experience: Inflatable mattress rides tend to be more leisurely, boogie boards more exciting. However fast one goes, the pool at the bottom cushions the blow as the ride ends.
The Rere Rockslide tends to be busy pretty much all day, but early in the morning it can be found empty and calm. The nearby Rere Waterfall, while not as exciting, can also be fun for water adventurers. People can walk along behind the water curtain (carefully, because the rocks are slippery), and though it cannot be slid over, some find it fun to jump into the pool at its base from the top of the falls. Eastwoodhill Arboretum is also nearby, and a nice place to walk around in nature.