Trekking and walking is moderately part of all tours. There is no need to walk a lot to see New Zealand's specific nature; most walks are under half an hour. If you feel like walking - no problem! - There are plenty of tracks here and there and this can be improvised during your tour.
National Parks are included in almost all tours. New Zealand is in fact so unspoilt that it can easily be seen as one huge National Park. The itinerary that includes the most National Parks is Splendour tour.
Meeting the locals is part of all tours, as we are often accommodated in small luxury lodges and we get to talk and socialize with their owners. New Zealanders are very friendly, and the small size of our tour allows us to have a real insight into their lives.
Many wineries are featured in Revisited tour; other tours also include a good introduction to local wines, but with less winery tours.
If you have a special interest in gardens and gardening, the best time of the year to visit them is October.
There are no real highways or motorways in New Zealand (except a few miles around some cities), and travelling around the country is done on small roads. The average speed is 40-50mph (70-80km/h).
The shortest suggested itinerary on this website is Wonders tour in 10 days (on North Island only).
The shortest itinerary including both North Island and South Island is Essential tour in 14 days.
Some travelers try to visit New Zealand as an extension to Australia, or to tour both countries at once. If you do that, you run the risk of being frustrated twice. Both countries are very different (in fact, they are as different as two countries can be - they have hardly anything in common!) and each of them deserves at least 3 weeks to get an introduction.
The longest New Zealand itinerary on this website is Splendour tour. It is also the most popular. It lasts 25 days and covers both islands; its duration can be easily reduced to 20 days.