Yes, that was the post that got lost.

There are some caves where you can abseil down, float along an underground river in an inner tube (with glow-worms), then climb out the other end (with belay, thankfully).

I couldn’t remember the name, but I knew it began with “Wai”, so I looked on the drop-down of destinations on http://www.intercity.co.nz/. Ah. Fortunately, only one of them ends in “Caves”. Waitomo Caves.