What are the best vacation destinations in new zealand?

Planning a family vacation trip to New Zealand next year and was wondering if anyone had any thoughts, recommendations or travel ideas as to the best destinations in New Zealand. We are trying to plan for a four week trip.

I went to new zealand a few years ago and probably the most memorable and best thing I did was this boat cruise up and down a fjord. it was over-night, got on one day in the morning, got off the next day in the evening. but it was really great because they had kayaking and there were dolphins everywhere and the scenery was absolutely amazing.

I would recommended going somewhere in Fiordland, like Milford Sound which has to be one of the most beautiful places in the world. Its best to do one of the short cruises. Queenstown is great for extreme sports, jet-boating etc. If you like walking, the Routeburn track in Glenorchy is world renowned. If you go to Christchurch, its not too far to get to Akaroa and Hanmer Springs which are both quite popular holiday places. The Marlborough Sounds would probably be my favourite holiday destination in NZ. Dont know too much about the north island which is shocking really since I have lived in NZ my whole life!