They look like the remains of a ruined castle in the high country of the Southern Alps. They are limestone outcroppings that weirdly punctuate the landscape. It looks as if an ancient megalithic civilization once lived here. They comprise the Castle Hill Scenic Reserve, one of several similar groupings that appear in the area.
On Monday, we arrived past the noon hour on a beautiful, cloudless day, a perfect day for casual exploring. A half-mile walk beyond the parking area leads to the rock formations. There are several worn footpaths that wind through the area, one leading up to a grouping on higher ground that from a distance looks strangely like Stonehenge perched on the hilltop. You can enjoy the park hiking (called tramping in NZ), rock climbing or mountain biking. With a little rock scrambling, you can get gorgeous views of the terrain, which is not in the least flat.
It really is wondrous to imagine that this entire area of limestone was at one time submerged in an ancient sea that millions of years ago was raised up to its current elevation of 700m (2300ft), the result of subduction between the Australian and Pacific plates. Heavy erosion combined with structural crustal deformation over the last 20+ million years created the fascinating outcroppings we see today.
There is another nearby attraction. Just a few miles east, Cave Stream Scenic Reserve features a 362m-long (1190ft) cave, which is pitch black and is wet the entire distance, including a deep pool with a 3m-high (10ft) waterfall.