Find your way to the start point by driving down to the Whakapapa River from Owhango, following the road through the Ohinetonga Reserve for about 2km. You can park at the bridge and walk from there, or alternatively also drive the few hundred metres further to the pumice pit (quarry) and start your walk from there. The cache location is a little more than 200m higher than the pumice pit, and the walk is a little more than 2.5 km in each direction.
From the pumice pit, head south up through the narrow pumice "gut" for the first minute or two, and then follow the track for about a kilometre, past the small waterfall and over the stream. Head left through a small clearing and up the less well defined walking track at the first reference point ("start of climb"). If you reach the cliff dropping down to the Whakapapa River (location of archived "Backseat Booty" cache) then you've gone too far, but I'd suggest this view is worth the short diversion in any case!
The climb up from the first reference point is quite steep but also not too long. At the top of that short section you'll turn left onto the track heading up the ridge to the east. This is mostly fairly easy going and quite well defined but you may need to cast around on a few occasions. Keep an eye on your GPS as you near the end point as you'll need to leave the track at that point and walk through the bush from a small clearing for about 50 meters to the south (towards the sound of the waterfall). Older GPS receivers may struggle under the bush so keep your wits about you to avoid getting disorientated or lost! (You're on a well defined ridge though so shouldn't stay "lost" for too long.) Get a good fix in one of the small clearings near the end and save a waypoint to help.
There is also an alternative route which involves following the road some kilometres further from the bridge and then going up the (quad bike quality) track to "the top of the skids" and then onwards to Deep Creek. Depending on your mode of transport, this could shorten the walk by quite a bit but also requires something like a quad or mountain bike, and willingness/skill/fitness to use your vehicle on the fairly rough tracks.
The cache was originally just a film cannister with short piece of pencil, paper, and a ten cent coin, hidden under a piece of bark on a stump. In January 2019 the original container and log was placed inside a much large container along with a new log book. From the cache location you can see a waterfall to the south. The best viewpoint is nearby, head about 15 meters to the west, and then climb down and towards the waterfall Do this very carefully - it's steep at the end with a bit of drop, and could be slippery, especially if wet!
If you have the time and inclination, the Owhango water supply dam is about a kilometre further upstream from the waterfall. To get there, continue up the track to a quad bike track, then right (south), across Deep Creek, and then after a few tens of metres turn left (east) up another track that parallels the stream up to the dam.
Make sure you tell someone else where you're going, and probably best not to do this on your own unless you are confident of your abilities in the outdoors. Enjoy!