A young caver from Waitomo in the early 1970s, Van Watson, was enjoying a night in with friends when they decided to adventure in search of the deepest cave in the world.
"We were in Tākaka in a very old woolshed on a very rainy night and it was New Year's Eve, so there was a whisky bottle somewhere. We were all enjoying each other's company so we decided to head off on our quest [to Papua New Guinea]," he told Kathryn Ryan.
He went on to lead a group of 23 cavers to the central highlands in PNG to find limestone beds rumoured to have the world's deepest caves which had never been explored.
The journey involved tramping over a nearly 3,000 metre high pass, through tropical jungle, dealing with blood-sucking leeches and a muddy track that could swallow a caver and their pack - just to get to the cave system.
Forty-seven years after the expedition, Watson has written a book about the extraordinary trip and those who were part of it, with images by fellow caver Paul Caffyn.
In the late 60s, a lot of mountaineers would hone their skills in New Zealand and then head to other countries to climb peaks, Watson says.
"So there was a history of doing something at home and then going to do something overseas."
Having heard about deep cave systems in Papua New Guinea, it seemed like the obvious choice for his crew.
Watson moved to Papua New Guinea when he was 21 and got a job in the bush. It took about six months before he got himself to the highlands.
"It was getting to grips with how to move through the country, how to get aviation up there and just getting through the certain nuances of working with the local people in very remote areas."
He was there for two years before he and a few others found the deepest cave in the Southern Hemisphere.
There'd been talk about big limestone beds out in the southern highlands of Papua New Guinea, he says.
"I was listening to our work radio at night checking in with the crew and I heard another company broadcasting, it was an oil expedition company, and they were up near the Lavani Valley. I got to talking to their head geologist and he said if I could find my way to their bush camp, they'd give me a flight in the helicopter over the area that we were interested in so I could take photos."
He flew over the remote area, but the military wouldn't let them have any aerial photos. What he did see though were sizeable streams flowing into bluff rock outcrops and reappearing in the valley area 3000ft below - a sign of a deep cave.
"It wasn't until the group were three weeks away that we got the aerial photos. We'd already tried to walk into the area once but the whole area is just hundreds of square miles green and there's one dotted line of a track going through to Nomad River and a couple of high points."
They were still cutting their way through the area, and cutting in a track, when the rest of the group flew into Port Moresby from Australia and New Zealand.
"The first couple of days we were on an established track that different patrols used, both military and government communication patrol. We were on that for two days and then our cut track to the north, that took another two days."
There were 23 cavers and ten porters at the site which was at 9000 feet. Splitting up in to three main parties, two field parties, they began their descent. There were three main cave systems they were exploring.
It was a mixture of abseiling and chopping vegetation to even get to the streams that entered the caves, Watson says.
Only in the past 30 years or so has there been equipment specifically designed for cave exploration. Before that, Watson says, you'd end up with a hodgepodge of alpine gear and roadworkers gear - anything that did the job.
"It was mainly back on the track on the way in and we'd noticed a few shafts on the bush there and that's where we got our main deep caves. We got two caves down to 300 metres."
The first group would explore to about halfway down the cave and the following day one of those people might stay on the journey and another two or three people joined them, he says.
"When you get to a pitch you either tie the rope around a decent bit of rock or you belt a bolt into the wall...you could clip a hanger and carabiner onto that and mount the rope onto that.
"You'd abseil down the rope and then keep on going down and when the cave finished you had to go up all those ropes again to get back to the surface.
"When you get to the deepest point in a cave you're usually quite disappointed because it stops going anywhere."
Caving isn't about repeating other people's journeys or perfecting your skills, it's about exploration, he says.
"When a caver climbs something, it will only ever be climbed once. Once they're at the top of it they'll smash a big bolt in and hang a big rope down and that's it."
Watson was about 23 at time, and he says following the expedition there wasn't a lot of time to reflect - he was straight into something else.
"We've been busy since 1973," he says.
Watson will be speaking about his book at the Mountain Film Festival in Wanaka next month.