Coming up the long hill behind the village of Acklam in the Yorkshire wolds, I stopped the bike and lay down among the scarlet poppies. The sun was truly hot for the first time in the year, the land shimmering in haze. I lay down my straw hat and prepared to snooze. This was my kind of bicycle training session. Nothing to it.

At some point later I heard a swish of tyres swooping down the lane towards me. I sat up and watched as a phalanx of Lycra-clad road bike titans swept past in a blaze of product endorsements. No one looked at me, or if they did I couldn't tell as they were all wearing sun visors. In a second they were gone. My peace was ruined. My peace of mind that is.

I telephoned my brother, Chris, who is into road bikes. "I've come out for a ride because I've been given the chance to enter a cycle event," I said. "It's called the Étape du Tour."

There was a long silence. "You are joking?"

"No, it's in a couple of months – in the Pyrenees somewhere."

"That's the toughest amateur cycling event in the world," he said authoritatively. "People spend years preparing. I think this year's route follows the hardest stage of the Tour de France: the Col du Tourmalet – also known as the Assassin. More than 100 miles and over 4,000m of climbing. People die."

I lay back in the poppies. "So should I take the shopping basket off?"

There is, I had discovered, a whole world of sporting travel options: marathons, triathlons, swims and cycle rides – challenges waiting to be taken up by those who want a trip with bite. My way in to the Étape, open to anyone on production of a doctor's certificate of good health, was to apply through the UK charity Get Kids Going, which specialises in placing competitors on events of their choice, in return for raising money for disabled children. There were dozens of other, equally exhausting options around the globe, but the Étape was the one for me. Not only is 2010 the centenary of the Tour de France taking in the Pyrenees, but the Tourmalet was the ultimate, the greatest, the man-eater.

"Yes," agreed my brother, "but popping down to the shops on your rust-bucket is not training. You've got to get serious."

The world of road bikes, I quickly learned, is definitely serious. David Ward from Giant Bikes talked me through chain sets, frames and cranks until my head was spinning. Then he got on to calories and ionic balancing.

"It's going to take you 10 hours," he said, "so nutrition is crucial."

I shrugged. "Maybe take sandwiches? Local patisserie?"

David gave me a withering look. "You'll need energy gels and high- calorie drinks. They'll give you at least 10% extra."

I smiled politely. Consumerisation, I thought. My Central Asia-specialist friend Bruce Wannell put his own spin on it: "You want tarkhan, the mix of dried mulberries and walnuts used by Afghan fighters – it's the snack food that defeated the Russians." Next time we met he handed over a large bag of it. "With the compliments of the Panjshir valley."

My first foray on my superbike did not go well. Riding along at walking pace, I turned to look at the dog – he'd insisted on coming along – and the front wheel dived from under me. As I went down my left knee gave a nasty click and I momentarily blacked out.

When I came round I was lying on the ground and two men in cycling gear were looking down at me.

"Clip-on pedals – lethal," said one.

"Worth 30% extra on hills," observed the other.

Word of my little mishap spread and people rang to offer advice:

"Don't worry. French roads are much safer – better tarmac. That's worth 3% extra."

"Shave your legs for a 2% speed advantage."

Adding up all my advantage points, I discovered I was almost at the finish. But then this confidence – so generously donated – was snatched away with a simple, but terrifying, refrain: "Two months' training! At your age! The Broom Wagon is gonna get you." The broom wagon is a nasty cycling institution where the stragglers, pootling along quite nicely, are suddenly swept up and out of the race for being too slow.

But despite my burgeoning broom wagon fear and a sore knee, my pre-Étape training was going well. I enjoyed my rides along lovely back roads of the Yorkshire wolds. I saw roe deer standing by the lanes, owls watching from fence posts; a weasel almost ran under my wheel. I noticed how these roads were constantly criss-crossed by small creatures: beetles, frogs, lizards, caterpillars and, on one occasion, a foot-long slow worm. The days went by too fast. Two weeks before the Étape, I managed 100 miles in seven hours. On the television I watched the first days of the Tour itself. Men and machines in a catastrophic tangle – a reminder that no amount of training can prepare for everything.

"This year's Tour," the commentator said, "will be decided in the Pyrenees, probably on the toughest stage, the Tourmalet."

My local bike shops in York, Cycle Heaven and Fulford Cycles, helped calm my fears and gave lots of useful advice. By mid-July I was as ready as I would ever be. I dismantled the Giant and took the train to Toulouse, then a hire car to Pau.

At 5.30am on the big day I headed in the dark towards town and the start. There were cyclists everywhere, all rushing to get to their starting positions. My number was 9,955 in a field of 10,000, so I was at the back. A car cut across me. Some drunks shouted. I touched the kerb at 20mph and suddenly I was skidding along the road on my side. People ran to help and an English voice shouted a commentary: "He's bleeding! He's getting up. He's worried about his bike ... Oh, his bike is knackered."

A local twisted the handlebars back straight. "Are the wheels buckled?" No, it was just the brakes that had been knocked. Together we adjusted them. I got back on, blood trickling down my leg and arm.

At the start I was still early enough to claim a front position in the pen for the last 1,000 riders. The atmosphere was electric. I felt like first-world-war cannon fodder about to go over the top. There are so many routes to failure: a mass pile-up, bike breakdown, or that defect in your heart that will only come out in extremis on the last climb. Mark from Australia was white-faced: "It's not fear," he claimed, "just zinc."

Each had a tale of fortitude to get here. There was Daniel from Sydney who had a cougar run out on him when he was training in Colorado. He also had a multiple fracture of his forearm after a crash, set in a bike-friendly cast by his understanding doctor. Chris from Teesside had trained on the same hills as me. "Two months' training?" he said sceptically, "you'll never make it." But we all shook hands and wished each other luck.

Seven o'clock came and went, but we weren't moving. At half past we rolled across the start. Then we were shifting, sweeping down Pau's streets, part of the oldest Grand Prix circuit in the world, past the train station at 30mph. Already there were casualties: bloodied men sitting on the verges, bikes twisted. We crossed the river and I was enjoying myself. The early sun was breaking through the trees, and villagers were standing by the road ringing cow bells and yelling "Courage!" A man played an accordion. Everyone was out in the squares, by the fountains and old churches.

We started climbing, but this was just a lung-opener, not the real thing. At Escot I was 20 minutes ahead of the broom wagon, but then we turned uphill, a six-mile slog up 8oom to the Col de Marie-Blanque. Any chatting stopped. Some riders got off. Then, half a mile from the summit, there was a crash and everyone had to dismount.

Then came another baptism of fire: the big descent: swooping down through the trees at breakneck speed. Within minutes my forearms were aching from holding the brakes, so I just let go and joined the madcaps. The result was total wild exhilaration. Under the trees the air was cold and whipped tears from my ears.

The feeding station at the bottom was a gleeful spree of complimentary bananas, flapjacks and water. I'd already been munching my tarkhan and it was working fine. With the first climb over and some food inside me, I really began to roll. We were in the foothills of the Pyrenees, and early clouds lay below us in the valleys, high peaks looming ahead. My head emptied of thoughts and worries. I thought of nothing. My existence was only the click of the gears. I was meditating at 20mph.

As we climbed the second challenge, Col du Soulor, I broke the silence to chat to Malena, a Danish woman.

"Why are there so few female riders?" I asked.

"It's becoming more popular," she said. "In France Jeannie Longo is still a champion rider and she is over 50. Women are starting to realise that cycling can be great exercise for them."

After Soulor came another epic descent, mile upon mile of fast looping roads and beautiful high Pyrenean villages. But at 80 miles we were heading up in to the mountains again. At the last food stop, the celebratory chatter of the early stops had gone. Everyone was worrying about the final climb: 1,600m without a spot of shade. I ate flapjacks, oranges, apples, cake and the last of my tarkhan.

They say a rider can burn 10,000 calories on the Étape, and for many it is just too much: the muscles simply run out of energy and can't get any more. At that point you stop. Cyclists call it "bonking". And on the Tourmalet, once you've bonked, the only way back is in a broom wagon. I was doing well though: 40 minutes ahead of the broom.

The climb started gently, curling alongside an icy blue river fed by streams tumbling down the hills. Many riders stopped to take a dunk. Imperceptibly the gradient increased. I was on my last gear and out of the saddle every hundred metres, but there were still 12 miles to go. My speed dropped to 4mph and then 3½. Some riders were lying in the shade, asleep. Some were being attended to. Most, however, were just grimly going on.

The final three miles was sheer torture. The Tourmalet towered over us, its pale grey crags seeming never to come any closer. A mile from the top, I simply came to a halt and was about to topple sideways when a spectator grabbed me. I sat on the grass, admiring the hillside covered in blue irises. Someone poured cold mountain water over my head. I fumbled in my saddlebag and found my last resort: one of the energy gels that I swore I wouldn't use. It tasted like heavenly nectar. I got up and back on the bike. The finish came at 2,115m and when I crossed the line, I had been on the bike for 11 hours.

I collected my medal and my food bag. Some people were celebrating, hugging each other and screaming, but I just sat down beside another competitor, who was curled up in a deep peaceful sleep. My brain had not yet started working and I was enjoying the dreaminess, a reverie tinged with a melancholy sense that this whole grand enterprise was over and ordinary life would soon resume. But then a voice disturbed me. "Kevin!"

It was Chris from Teesside. "I take my hat off to you," he said, "I really didn't think it could be done on two months' training."

Well, I say it can be done and it should: for the thrill, the excitement, the sense of achievement, the meditative pleasure of rolling through magnificent mountains – and the 20lb of excess weight I lost.

When the Tour de France finishes in the Champs Elysées tomorrow, I will be cheering them on, and afterwards, maybe I'll get the bike out and head for the hills once more.