The brochure shows long-haired girlies sitting sheepishly on the "quad machines" (four-wheel mini-tractors which hurtle round the countryside). One teenager is wearing shiny leather brogues. Another holds the steering bar primly. "Thousands of acres of unspoiled trekking country" the brochure gurgles, "across some of the most spectacular scenery in Mid-Wales".

I am not a natural driver. I passed my test a year ago after more than 100 lessons and have not driven in Britain since. But my companion liked the brochure so I packed a pair of old walking shoes and got on the train to Wales.

The scene at the Dovey Valley Power Trek and Shooting Ground, Machynlleth, was straight out of The Deer Hunter: groups of silent, mud-stained men in khaki gathered around a scruffy log cabin. I was just about to throw my hands up and surrender, when one of the organisers came over. "Go and get changed," he said.

All the best gear had gone by that time - there were only crotchless trousers and battered helmets. But it was pouring with rain, so rubber trousers were imperative. I had to wear two pairs as there were no complete ones left. Then it was a quick run through the rain to the portable loos (nerves), then back to the van were everyone was waiting.

We were the "nursery class": children, women and the old. Most of them had done "power trekking" before. They chattered about "exhilaration", "feeling free" and the "power" of the vehicle. One woman had her face covered with make-up. Another was six months pregnant. The sight of the 15 or so quad bikes was a warning of what was to come: they were parked there, like sad horses, plastered with mud while the rain bucketed down.

The "instruction" lasted about a minute (these are the brakes, this is the electric push-button starter, here is the gearstick, this is how you accelerate) and for the next hour the 10 of us laboured round the nursery ring: some flying, others crawling. My quad bike stalled every two or three minutes. A female instructor came over to help, but made the mistake of stepping in front of me. At that moment the bike started, leapt forward and hit her. I was more shaken than she was. But then, she was an Australian.

There was also the hideous embarrassment of being the only one to refuse to hurtle down a steep hill. In the end I compromised: I slid down with the brakes on. For a second I had flashbacks to a time when I walked sideways down an entire ski slope in Finland. But no. This was Wales and I was the city girl holding everyone up.

As for the birds and the wildlife as promised in the brochure - there was not one to be seen. Perhaps the sound of stuttering engines, shouts, splashy puddles, skids and wails had frightened them away. Or maybe it was the relentless rain. The countryside was brown and sparse - dotted with sheep and truly beautiful. I just wanted to get of my quad machine, kick it over the cliff and walk. "We're going back to base," shouted the Australian. "Get in the van!"

I looked around. Everyone's faces were splattered with mud. They were smiling, and chortling about the magnificent bumps, the thrill of pounding through a puddle and the high of shooting down a slope with no brakes on. When we got back to base I looked in the mirror - my face was as white and clean as when I started. "You didn't enjoy it, did you?" the men said. "We can tell."

"Yes I did", I lied. But the game was up.

Back in the log cabin, the room was full of smoke and steam and sweat. All the men were sitting in clumps - about 50 of them - up from Birmingham, round the Midlands or local. Many of them had spent the night camping and the morning shooting and were now swallowing cheese sandwiches. They stared when I came in. It was time to go.

My companion had a whale of a time. He went out on the "most difficult" trek with "the most experienced men" and hurtled down galleys, through forests and along rock edges. At one point the man in front of him was tossed off his quad bike. My companion expected a broken neck or at least blood. But the man got up, adjusted his helmet and climbed back on. There was a revving of accelerators and the pack drove off. Hell's Angels in khaki.

Dovey Valley Power Trek, Brynmelin Farm, Llanwrin, Machynlleth, Powys SY20 8QJ (01650 511252)