Just down the road from Castle Hill / Kura Tāwhiti Conservation Area is an impressive 594m limestone cave, part of the Cave Stream Scenic Reserve.
There are two entrances to the cave, this one being by far the most impressive, a huge opening in the valley side into which it’s possible to enter a short way without getting wet.
The other entrance (where the stream enters but people exit) had some fascinating shapes and colours, and if you look closely on the left in the final photo a ladder for people to get out.
The landscape above ground isn’t bad either, typical of the scenery on the wonderful SH76 running from the Canterbury Plains to the West Coast via Arthur’s Pass.