The Pancake Rocks are great but can be a bit disappointing if the tide isn't right to see the blowholes going off.
I lived at the mouth of the Punakaiki River for 2 years and used to kayak through the caves under the rocks at low tide.
Lots of Hectors dolphins to play with too.
Christchurch was home for about 14 years too. I went there in 81 mainly for the music scene,and because it reminded me of 'home' (England). I was a punk/skin in those days and Chch had a huge punk scene in the early 80's.

Steve