West Edmonton Mall boasts the world's largest indoor waterpark with a 1.8 hectare wave pool. I preferred the extreme slides: Nessie's Revenge, Sky Screamer, Tropical Typhoon. Two of them bumped my head, all were lightning fast. The typhoon slide really was more like a giant toilet bowl flush into 10 feet of water. I went upside down and backwards into the drop. Nessie's had three bumps and I'm sure I was airborne significantly on the third one. Sky Screamer doesn't quite scare as much as Disney's Summit Plummet at Blizzard Beach but combine all three and it was more fun overall. When you go with junior high kids you don't have time to think about mortality, you just fly from one crazy slide to the next.
I recommend it highly.