This is an example of a small coastal sand dune formed by the action of wind and waves (and dare I say a bit of human intervention in the way of civil engineering) on beach sand. Thankfully you can approach this cache from a direction that does not require you to walk over the dune and potentially damage the fragile flora and fauna that have made this niche habitat their home!
take some time to have a look at the sculptures in the area or perhaps let the geokids loose on the nearby playground :D
The cache itself is a fake rock when placed only contained a log book, you will need a writing stick. Happy hunting!
For those more scientifically minded this publication by DOC may be of interest in identifying the species growing in the area: Wellington coastal dune plan