The coordinates given on this page are not real - don't go there! The three caches are:
Cache coordinates for these are as given on their web pages.
The point that has equal distance from three other points is the centre of a circle that goes through those three points. It is called the Circumcentre. This only works in Euclidean (planar) geometry (ie, spaces that are flat, not curved) and so the Latitude/Longitude coordinates need to be converted to grid coordinates (where distances are the same in any direction). You can convert to Map Grid here, or your GPS unit may even display/convert Map Grid for you.
The idea is to use a bit of maths to solve this one accurately. You can either use a ruler, protractor, compass to find the circumcentre by construction on a grid map, or even just grid papar; or work out the formulas that derive the circumcentre using some linear algebra.
If you need a map, the 260-R11 topographic map from LINZ is ideal, as it covers the area and has the Map Grid coordinate system superimposed making it very easy to plot points. But you can probably also use a large sheet street map. If you use the formulas, then you can use any grid system (eg, NZ Transverse Mercator), although I've used Map Grid coordinates if you want to get the same answer as me 
. Convert back to WGS 84 if you can only enter geographical coordinates into your GPS.
You can drive to the cache between 7am and sunset. A good place to bring your dog. First find the boulders shown above - the cache is 10 paces up the hill, and is a 2.2 litre plastic container painted green. It contains a clue for the Somewhere in Auckland cache (and also Ring Around Pupuke).
This cache was inspired by evilC 
- so don't blame me 
.
You can check your answers for this puzzle on Geochecker.com.