As a local who has completed two full tours of the country, I have to say there is no other part which quite creates the sense of travelling into the prehistoric past the way Te Wahipounamu does.
It's so simple to find a quiet spot where you can contemplate how little the landscape has changed here over the aeons, to get some perspective on how damaging the presence of humans is - and how important it is to ensure areas like this remain free of that damage. Then there is just the sheer, raw natural beauty of the place - it's a cliche to say it leaves me speechless, but that truly is the effect.