Intrepid Nicolas Barth was kind enough to take Nial and me down in his caves near Dunedin a couple of years ago. It was really amazing... and kinda scary! Nic is incredibly brave to have explored these caves to this extent. I made a little 3D model based on photos from the one day I was there and am delighted to see it made it into the video (appears at 1 minute 30 seconds).
Here's the original video I sent Nic: