Disney World has two, Blizzard Beach and Typhoon Lagoon. Blizzard Beach has Summit Plummet, a 120 foot high water slide. I haven't been in for a couple years, but when I was there last it had a speed trap at the bottom so you could tell how fast you were going. 50+ miles per hour is typical. It's got a long trough at the end to slow you down. Typhoon Lagoon has a wave pool, and I've seen groups rent it after hours to teach surfing. Both have a lazy river ride where you sit in a tube and just float along at about a slow walking pace. That's my favorite, I like to just drift along, relax, and enjoy all the neat plants I'm floating past.