The track to the hut is a side track off the main Koranga Tawa loop.
A directional sign marks the side track up to the Kahunui hut. From the Tawa hut to the Kahunui hut takes around 3.5 hours. The track has some benched and marked sections, but mostly is walking alongside the river.
You'll need to cross the river several times. A large orange marker indicates the side stream where the Kahunui hut is sited. The hut is 5 mins from the Kahunui stream.