I really did begin with absolutely no intention of doing a 15-metre leap into freezing cold seawater. But there was Jethro, our guide, a factor I had not bargained on. The man ought to be a stage hypnotist: his calm voice never rises beyond a casual tone, always giving practical instruction that seemed so simple, so easy to follow. "Look straight ahead."
No problem. Looking down was definitely not a good idea.
"Keep your arms across your chest."
Yes. What could be simpler? Feels safe and protected.
"And take one big step away from the ledge."
We had come to Pembrokeshire to stay at a place called Fforest – the Welsh double-f making the sound "f". There had been talk of a sport called coasteering, which sounded intriguing.
We drove towards the coast – myself; Niall, 14; Maddy, seven; and Wilf the dog, one – and found our destination in woods on the bluffs above the river Teifi about three miles from the coast (and some glorious beaches).
There James Lynch and Siân Tucker have built an upmarket camp. But if camp makes you think of a simple tent, think again. Here, you might be sleeping in a geodesic dome complete with logburner, or in a "threepi", or, in our case, not in a tent at all but in what James and Siân call a crogloft. This is a cosy dwelling converted from stone farm buildings with sleeping chamber and sitting room, plus a sturdily retro outdoor kitchen – all blue and white enamel, cast iron and worn wood – that they have just added this year.
Everything is designed to ease you out into the fresh air. If you have kids, you will quickly know everyone on site. If you don't, you can choose to remain secluded and private. My family soon settled in. Wilf got acquainted with the two cats, chasing them up adjoining trees, then standing guard. Maddy made friends with Bea and Minnie next door (13 and 10 respectively). Niall fell into a deep coma on the bench. He is in the iPod stage of development: the only signs of life come, paradoxically, when the battery runs out.
Next morning Wilf discovered the farm dog, Arrow, a black and white male collie, which – in youthful but well-meaning confusion – Wilf attempted to mount. Maddy played with Bea and Minnie. Niall could not be roused.
Down in the breakfast room, James told me how he came up with the idea of Fforest on an extended trip to New Zealand. "It was something in their approach to hospitality," he said. "Just warmer and more sociable. I decided to import it to Wales."
Hence the communal table for breakfasts and, occasionally, evening barbecues. There's a snug sofa area, too, and even an outdoor cinema to bring everyone together: it's a big old sail strung between two trees where James projects film classics on summer evenings.
James continued: "The farm here has 200 acres, and we're next door to a superb wildlife reserve.
"We do canoeing on the river. If you're lucky, you can see otters down there. Or get up early and walk down to the meadow, where you might spot the deer."
Niall appeared. He had been growing a moustache all night and the poor boy was shattered. He slumped into a chair, his iPod life support system giving out a feeble hiss. A large proportion of the food on the table – and there was a lot – disappeared inside him, with minimal discernible movement on his part.
"Good appetite," said James appreciatively. Niall grunted, which I imagined did not register very highly on James's Kiwi sociability scale, though he was far too affable to show it.
From the kitchen I could hear Maddy's imperious voice, addressed presumably to the cook: "And where do you keep your biscuits?"
James turned to Niall: "How would you like to have a go at coasteering? You put on a wetsuit and explore the coast. Jumping in, swimming, climbing. . ."
Grunt.
"I'm sure he'd absolutely love it," I said, over-compensating on the enthusiasm front, as parents do.
So it was decided. We would head out towards what is known locally as the Blue Lagoon at Abereiddy.
Down at Abereiddy beach, we met our guide, Jethro, and a small group of potential coasteerers, plus, to Maddy's particular delight, Bea and Minnie.
I'd been worried that she might not go for the idea of plunging into freezing cold seawater but, with Minnie and Bea around, I felt renewed confidence. "Big girls", in my experience, are the crack cocaine of a small girl's life.
The water, I knew, was going to be very cold. Maddy was wearing two wetsuits and, as soon as her toe touched the first little rocky fjord, she drew back, saying, "No, I'm not doing it. Definitely NO!"
The others, six of them, plunged in and splashed across. Maddy and I sat watching. The kelp swayed invitingly. We waited.
The others climbed out on the other side. "Oh look," I observed slyly, "Minnie's done it and is climbing out."
Minnie turned and waved. "Come on, Maddy!"
Without hesitation, Maddy jumped. I followed.
The sea in Pembrokeshire, everyone agreed, had the gorgeous turquoise limpidity of the waters around the Seychelles or Maldives. It also had, in early spring, the brutal cold of the Arctic.
My hands, gloveless, felt as if they were being beaten savagely with ice-cold hammers.
However, after further climb-outs and plunges, I started to feel that it wasn't too bad. In fact, I no longer felt anything, having reached the stage that is known in Yorkshire as "numbed up".
We made it around to the lagoon – actually an old slate quarry beside the sea that has had the last remaining rock barrier blasted out to make a spectacular and serene pool about 100 metres across. Jethro soon had the group doing jumps – low ones initially, then bigger.
I took photographs. I was not doing any of the leaping.
It was then that I saw Niall scrambling up a small rock pillar to gain extra height. It must have been a good 15 metres above the water. He didn't look like a man in a coma any more. It was a display of bravura, I thought, and there wasn't a chance in hell that he would do the jump.
Niall jumped.
Three minutes later I was admiring the view from the top. The competitive instinct between fathers and sons was ridiculous, but unstoppable. The view was impressively terrifying. Niall, swimming far below, appeared like a tiny jeering prawn. At that moment, I still had no conscious desire to jump, but then Jethro was next to me. His gentle voice started on the preparation.
"Look straight ahead."
It was like a countdown.
"Keep your arms across your chest."
Yes. What could be simpler?
"And take one big step away from the ledge."
I remember thinking on the way down, wow, there's even time to think. Maybe I should breathe ... As I inhaled, I hit the water. It was, to be honest, an awesome crunch.
I felt my spine do something like a snooker ball trick: clack-clack-clack, very quickly. Then I was swimming on the surface and grinning. I could still move all four limbs, probably still feed myself and go to the loo without catheterisation. Most of all, I was not in a coma, and neither was Niall. He was out on the shore, chatting with Jethro like a man recently emerged from suspended animation. Leaping into cold water had jolted him out of his teenage catatonic trance.
Back at Fforest we enjoyed the barbecue that evening. The little bar, the Y Bwthyn, was open, and the fire was lit. Maddy had learned not to raid the kitchen cupboards. Niall was talking to Bea and Minnie's dad about Top Gear. We were almost civilised. Perhaps this Kiwi hospitality thing, combined with regular applications of cold water, can actually work?
• A week at Fforest (01239 623633) in summer in a two-bedroom tent with outdoor kitchen and deck costs from £365, weekend stays cost £215. Croglofts sleep up to four and cost from £750 a week, £395 for weekends. Activities include woodland crafts, bushcraft, coasteering, kayaking and archery
