http://www.doc.govt.nz/parks-and-recreation/tracks-and-walks/southland/te-anau-area/routeburn-track/plan-and-prepare/fees-and-bookings/
You have asked this on Australias site. New Zealand has a different site. I haven't walked it but have been to other tracks. I think the Routeburn would be a super walk . It is strictly run by the National parks and they have many rules which you can read on the site I have given you. Fees apply and you can be fined for doing the wrong thing