The Routeburn and Milford Tracks are two of the 9 Great Walks of New Zealand. The map below shows their location on the south-west coast of the South Island.
The Routeburn track is a 3 day, 2 night trek of 32k from The Routeburn Shelter to The Divide
The Milford Track is a 4 day, 3 night walk of 53.5k, although GPS measurements by many walkers put it at 57k.