The Taniwha is a mythical Maori water monster, not commonly seen these days. However I'm sure there is one very close to where this cache is hidden! There is a dark vent from which there is a constant roar and a blast of air and mist. Luckily this vent has a locked grill to protect innocent visitors. There are also many warning signs signs about the dangers of entering or venturing too close to the nearby Whakapapa River.
Replaced and relocated in January 2019 - hopefully not too hard to find as long as the monster doesn't get you first...
The access road from SH 47 runs through farmland. The status of public access is currently (2023) unclear. You may need to contact the owners/manager before arrival to be sure. The road was built originally to provide access to the structure near the cache location, not the farm. Note also that there are more warnings about the road being unstable (there is some subsidence) near the end when it descends to the river. It isn't a long walk from that point if you prefer to avoid driving past the sign but I have never had any problems.
My understanding is that public access via the Whakapapa Intake Road to the Whakapapa River is supposed to be guaranteed but a relatively recent change of ownership may have resulted in this not currently being honoured.
See the following link for more information: https://www.tongarirorivermotel.co.nz/whakapapa-intake-road-closed/