I had a quick jaunt up to an observatory in Tekapo.
Afterwards, I made my way to Castle Hill. This spot is known for its great bouldering, though not much was happening the weekday I was there.
There were, however, large boulders spread out.
A few kilometers north of there, there is a half a kilometer long cave you can walk through. You start at the bottom of a stream in waist-high water, and make your way in pitch-black upwards and against the stream. The walk is pretty relaxing, but there are two points you have to shimmy up opposing walls.
I did not heed the recommendation to have your hands free, so I struggled a bit with this part. I had a brief second where I thought I would be trapped underground forever, but then it passed.
Some nice Germans took my picture before I went in, as I was trying to put my hands in my zipped pockets.