Very fun activity in Rotorua... They have wet zorbs and dry ones, I recommend the wet because it's all part of the fun. They have hot tubs you can relax in until it's your turn to zorb. Good fun and lots of laughs.
The wet Zorb with a partner is one of the funniest things we have ever done - running down a hill like a hamster in a cage while desperately trying not to trip over the other person is an experience that has to be had oneself to appreciate.
I'd mark it higher except for the tourist prices which mean you can't necessarily afford to go on it as many times as you'd probably like to :D