While the pros were enjoying a well-earned rest day on Monday, over 7,000 amateur (and some not so amateur) riders were getting a taste of what it's like to ride the Tour De France. Or, as the thousands I witnessed would probably testify, getting a taste of why they aren't currently riding the Tour for a living. That taste consists largely of energy drink, sweat and suffering on a monumental scale; and anything up to nearly 13 hours in the saddle.

David Millar, in his Tour Diary for Bicycling.com, admits to a "dark joy" at "knowing they are experiencing what we get to endure on a regular basis" over his close friends and family taking part. I spoke to his manager James at the first feed station and his huge grin suggested he was still enjoying it, but then there were still four climbs to go.

At that point, having already crossed the Col De Port and enjoyed a spectacular, if a little chilly, fast descent for around 40km everyone in the groups around me still had a broad smile and a respectable hope of finishing. The sight of such a number of cyclists snaking back along the road is quite magnificent, especially near the top of the climb where you could see them all the way back down the valley.

After the feed lay the business end of the day, which meant it was time to get into a good group and prepare for the onslaught. I managed to get in with my clubmates Jonathan and Peta on a large, reasonably fast-moving group which hauled us up to the start of the four climbs with a sense of trepidation tangible among the riders around us.

The Col de Portet D'Aspet was hard but not ruinous. As we worked in the group and picked up wheels I felt good despite my ever-decreasing average speed. For reference, I tend to climb with all the pace and grace of a tortoise on valium, a situation that hasn't improved considerably with training. Having put the gap between me and the broom wagon early on I had plenty to play with so was still a long way from clock watching.

The descent took us past the Casertelli memorial, a reminder that getting things wrong on those Pyrenean roads can be fatal. There were crashes on Monday, of which I saw the aftermath of two, as is usual when so many riders on the mountain, many of whom forget the necessary skills for getting off the mountain safely. It can be easy to forget that descending requires as much skill as climbing.

For me, there is no more joyous sight than a good descender. Greg Lemond was one and he no doubt enjoyed the day, getting round the 199km in 8 hours 21 minutes. That's a twice-Tour-winner, albeit not quite as trim as he used to be, so you can imagine just how long it would take the less talented of us on the course. The winner, a former pro with Saunier Duval finished in around six and a half hours. As L'Equipe noted, his achievement is largely a footnote to those of thousands of others for whom just getting to the finish was a massive achievement.

The Col de Menté followed immediately and was the first time I felt the suffering start to rise. This was the point where I moved from thinking about enjoying the scenery to concentrating purely on the road ahead. No more photo opportunities, just disciplined turning of the pedals and trying to keep my pace up on the flatter sections while forcing food and drink down to avoid the dreaded "hunger knock". I could hear the voice of Sean Kelly burbling on about it in my head, although that was mixed with the sound of my own heart pounding in my ears and the rasp of my breath. And Kate Bush's Running Up That Hill which helped me knock out a nice tempo.

At the top I had a chat with one of the many hundreds of French volonteers who manned the feed stations, encouraging and helping the riders along the way until Jonathan arrived looking like he had endured his own private purgatory on the climb. All the riders will no doubt join me in generous thanks to the locals who lined the road, filled bottles, encouraged and helped us all on our way. Personally, the level of encouragement only made me more determined to finish.

Another stunning descent led us into the decisive climb of the day, Port de Balčs, 20 hellish kilometres which would decide the fate of many. My friend Frank, who had given me a lift down, decided it would be a hill too far for him after nearly 140 already ridden. For many of the riders I saw on the way up, slumped in the shade or propped against their bikes with looks of despair etched on the faces, it certainly seemed that way. Like many others, I experienced total mental meltdown somewhere on the climb which required me to stop and gather up the remains of my composure during a toilet stop.

About halfway up I saw Carl in his BBC Sport jersey and we wished each other luck over the remaining distance. He had stopped to catch his breath and try to get his heart rate down a bit, something many riders found themselves needing to do on this climb.

Melted asphalt and a rubbing front wheel probably slowed me down more than I needed but I didn't have the mental wherewithal to deal with mechanical issues. I did however turn to my climbing inspiration, Robbie McEwen, for guidance and adopted an attitude of getting to the finish just inside the limit. With over three-and-a-half hours to climb in I made sure I used that time wisely. Had I tried to kick on I wouldn't have made it but by staying at a manageable level of agony I knew I could get to the top with time to spare.

The descent was worth the climb - hair-raisingly narrow at the top with corners where the only view was open sky, unobscured by safety barriers. I opened out down it knowing that I was now at the point where I could make it to the finish if I just kept going. The 9.7km of the Col de Peyresourde wouldn't seem too tough on its own but the cumulative effect meant it still took me about an hour to reach the top. As the "kilometre au sommet" markers counted us down, the sense of elation battled its way to the surface. The locals encouraged us all the way and I found myself struggling to to keep the emotion in check. About 100 metres from the top "The game is won, victory is yours. It is well deserved." rang out from one group of locals bringing a tear of joy to my eye.

The final descent to the finish was pure elation as riders drew stock of what they had achieved. I passed a few Brits I had ridden with earlier and we offered generous congratulations to each other. Coming into the final approach packed with applauding fans on all sides I grasped what it must be like to win a stage like this and remembered to zip up the jersey and cross the line with arms outstretched. On the other side of the line Dave Brailsford of British Cycling, recognising another Brit from my London Dynamo jersey, gave me a smile and a nod which was probably more that most finishers could physically manage. Certainly a smile of joy proved a challenge for me.

A massive congratulation to all who attempted it and in particular those who finished what will go down as one of the toughest Etapes ever.