The published coordinates will take you to a wooden sculpture at the Riverside Holiday Park, beside the Buller River at Murchison. I parked outside the camping ground but you will probably have no problems parking within if you are sensible and want to save yourself a few steps.
This is a multicache, so there is no geocache at the published coordinates. There is however a blue and white sign nearby. UPDATE: There is more than one blue and white sign in view, the one you want has 3 white words on a blue background followed by 2 blue words on a white background. Note what the sign says and use the letters (A = 1, B = 2 etc) to work out where the cache is. The cache can be found at S41 47.4M3 E172 20.Q80 where M = 6th letter and Q = last letter.
If your calculations show that the cache is around 600 metres away along the Buller River you are most probably correct. The cache can be reached by walking or can be driven to along a "country lane" the other side of the golf course.