Hey there! I live in Auckland NZ. The weather will be cold and probably raining in August but theres still lots to do. In Auckland you can visit the Skytower, it has a casino and a revolving resturant. There are night clubs in Auckland City which are awsome! There is Kelly Tarltons Underwater World which shows you some of the sea life. You can visit the Auckland Museum. You can go to Spookers which is a Haunted House (with actors). Rainbows End is our only theme park.
In Rotorua you can see natural boiling mud pools, and do the luge.
In Waitomo you could go Black Water Rafting. This means you go in caves in a rubber tyre, very fun. Might be abit cold in August but they do provide wetsuits.
You can also visit the many beautiful beaches, but you wont be able to swim because it will be too cold.
You could also head to Mt Ruapehu for some Snow Boarding.
There is lots to do! You dont need to plan anything before you get here because nothing takes too much booking in advance.
Hope that helps 