The Heaphy Track is an 80km (50 mile) challenging multi-day, remote back-country adventure ride. It is ridden for its awesome scenery, it wilderness charisma, its unique native forest, its coastal vistas, wildlife and because it's a great challenge needing advanced riding skills and perseverance.
It's a very popular hiking track, considered one of New Zealand's best. There are several back-country huts along the way but not a café or cell phone tower for many miles! Most of the huts have cookers and pots so you can travel light but...
The track is only open to bikers from 1 May to 30 September, winter, when this part of the planet can be cold and wet. Check the weather forecast before even thinking of starting this adventure!
In good conditions this track is exceptional. Here is the gush from http://heaphytrack.com/mountain_biking.html
"The Heaphy Track is the only multi-day ride through a National Park in New Zealand. The 80-kilometre course through the Kahurangi National Park traverses dense beech forests, expansive tussock plains and boulder outcrops of the Gouland Downs, takes in the limestone cliffs along the Heaphy River and through the nikau palm groves and white sandy beaches along the West Coast to Karamea."
That site is excellent and has a blow by blow description of the track with excellent maps and everything you will need to know to plan and organise your adventure. Be sure to check it out.
The Department of Conservation has also has an excellent page on the track here:
The track also has its own Facebook feed: https://www.facebook.com/HeaphyTrack
And of course google will find you oodles more information and pictures.
Huts have to be booked in advance and you can do it here: email@example.com or at information centres.
This is a trail you don't want to rush - it's one of those once in a lifetime adventures that you want to savour.