Drive south of Grenoble and then east on the N91, following the road along the valley and climbing steadily through Gavet and Livet to the village of Le Bourg d'Oisans. After a slight downhill stretch, there is a turn on your left over a bridge where the road doubles back on itself and winds up the mountain like a half-coiled rope. The road is marked as the D211, but to the gladiators of the Tour de France who will ride up it on Saturday and to the thousands who will cheer their every agonised thrust, it is known simply as L'Alpe d'Huez.

"If you are not intimidated at the foot of Alpe d'Huez, you never will be," Robert Millar said. "You go through every emotion on that climb. You feel angry, you can feel very good, then suddenly feel terrible. Physically you're on the limit all the way. The best you can hope for, if you're going well, is that you won't feel frightened."

Millar was the best climber ever to come out of Britain. He won the polka dot jersey for the King of the Mountains in 1984 and for several years matched wheels with the greatest climbers in the peloton, the Colombians and the Dutch, Delgado and Hinault. Millar was a true grimpeur; wiry, gaunt, single-minded, a man of great wisdom and precious few words who earned his keep on the faces of cliffs such as L'Alpe d'Huez. He hated the place as much as did Sean Kelly, who had a climber's heart in a sprinter's physique.

In 1984, Millar was in a group with Laurent Fignon when Bernard Hinault attacked in the valley before the mountain. Hinault turned and laughed at his fellow Frenchman as he sped off into the distance. But Fignon and Millar had the last word, relentlessly riding Hinault down on the climb to the swish ski resort quaintly advertised as the Juan les Pins of the Alps. Kelly was there that day too. Fifth over the Col du Coq, he was feeling pretty good in the group chasing Hinault into the foothills of L'Alpe d'Huez.

"On the first slopes I knew I was in big trouble," he recalled. "That climb was one of the worst experiences of my life." From being a contender for Tour victory at the bottom of the mountain, he was yesterday's man an hour later and 1,860 metres higher. Arguably, Kelly never recovered from his battering.

"It was all the stuff around Alpe d'Huez that made it so difficult," he recalled. "The people and the smell of the barbecues and the heat. I always remember there was bits of tin foil flying around from the people camping and the bloody motorbikes with the photographers watching your every twitch. So many times you had to slacken off on your pedals because you thought you might hit someone. It broke your rhythm."

Rhythm is at the heart of the climber's art. Mountains with a steady gradient, which require little change of gear or beat, encourage a regular tread. The 14km climb up Alpe d'Huez is not the longest on the Tour, nor with an average gradient of eight per cent is it the steepest, but since the great Fausto Coppi won the first stage there in 1952, the Tour's most revealing dramas have been played out through the 21 tortuous hairpins. For the crowds who flock like pilgrims to Mecca each summer and turn an afternoon's sport into a three-day carnival, the hairpins are the distinctive and most attractive feature of the climb, allowing unrivalled views of the theatre. To the riders, they disrupt rhythm and, as each one is individually numbered in ascending order, quantify suffering. On a good day, the climb should take 45 minutes; on a bad one, an hour or more.

"The first four kilometres to the village is the steepest, where it's hardest to find a rhythm," Millar said. "That's where a break might come. You're at 105 per cent there. Then there are a couple of relative rests, after four kilometres and another at about 10 before a nasty little climb just before the finish. It's OK when you're imposing your rhythm on others, usually it's the other way round. It's just 40 minutes of grovelling."

But it is more than that. Like all spiritual sporting homes, Alpe d'Huez unravels character not just in the cruel language of the stopwatch, but in the eloquence of expressions. Their hired hands long exhausted, contenders for ultimate yellow will find solace in every grimace, search longingly for signs of the weakness they themselves are trying not to show. Miguel Indurain's ability to mask pain behind a half-smile and dark glasses was critical to his psychological dominance of his rivals.

It was on Alpe d'Huez in 1986 that Hinault tried to break Greg Lemond. Hinault still claims he was only helping his team leader up the mountain, that he could have won the Tour had he wanted to. Lemond, the eventual winner, said Hinault was spent. The pair crossed the line hand in hand, a gesture of blatant hypocrisy by both men, but fringed with a mutual respect.

"Things always happen on Alpe d'Huez," Stephen Roche says. "It comes at the end of a long day, but you have to keep your wits, look around and see which climbers are there and who you can afford to let go. " It is where, in the accepted wisdom, Tours are rarely won but often lost, as Roche understood perfectly.

In 1987, the Irishman was locked in a struggle with Pedro Delgado. The previous day he had kidded the Spaniard into thinking he was going better than he was by riding alongside him not behind him. But Delgado was the better climber and Alpe d'Huez was his playground. Roche had to cut his losses, but not push beyond his limits and crack. By the end, he had conceded just 61 seconds and lost the yellow jersey, but done enough to conserve his strength for his epic ride up La Plagne the following day where Delgado's spirit finally broke.

"I knew I couldn't go with him," Roche, now a television commentator with Eurosport, recalled. "So I just had to keep to my own tempo and hope not to lose too much. It's often a matter of luck." A friend of his from Ireland had run alongside him on one stretch of the climb, offering encouragement. Roche recalled nothing. "You go into a trance, you don't see anything." A year or so later, Alpe d'Huez gained its revenge. Roche lost 22 minutes and shortly after went into retirement.

Stage 13, 204km from St Etienne on Saturday, will be no different. Sandwiched between the time trial and a Sunday stage which includes two ferocious climbs over the Col de Glandon and the Col de Madeleine, it will not decide the Tour, only cast a few illusions to the thin Alpine air and strengthen the resolve of the potential victors. For a climber, victory is enough. Alpe d'Huez is the true pinnacle, a passport to glory and reverence, not just the conquest of a mountain or rivals, but proof of heart and soul.

"There were some mountains, steeper than Alpe d'Huez, which I found much easier," Millar said. "I never liked that place, never felt comfortable on it. I always felt nature was going to beat me."