Riding around the south island would be awesome (apart from Christchurch).
We live in Wellington, in the north island, quite near to director Peter Jackson and some of the first Lord of the Rings movie was filmed not far from us on Mt Victoria
Unlike with motorbikes, NZ is very pro car. We are right hand drive like Japan but have no car industry. So we have free open import on Japan's used car fleet. After five years Japanese people pretty much have to sell their cars because older cars are taxed off the road.
You can buy a used Toyota here for about the price of a motorbikes annual rego! - so for a low pop country we have a hell of a lot of cars. Auckland is a nightmare. But the south island has amazing roads and hardly any traffic
