The story that a band of wandering Trappist monks stepped into Calvin Klein's limestone and glass store on Madison Avenue one day, and were so taken with its elegantly minimal spaces that they immediately decided to track down its architect and hire him to design their monastery is a myth. In fact the order's abbot came across John Pawson's work in a book.

But it is perfectly true that Pawson has designed a Cistercian monastery, and that it was consecrated in early September. And it is also true that the monks asked Calvin Klein to design their robes. He agreed, but they changed their minds when they realised that it might not be a good idea to be quite so stylishly turned out and to attract quite so much publicity for it.

The Cistercians have always treated architecture as a reflection of their principles of simplicity and self denial.

Five years ago, Pawson found himself taking a delegation of Cistercians on a tour of his famously empty house in London, only for one of them to express his polite concern that it looked a little austere for a monastery. When the monks came to see him, they brought with them a list of requirements for the design of the monastery that is an engaging mixture of the practical and the spiritual.

Pawson has translated them into Novy Dvur, the first monastery to be built in the Czech Republic for more than half a century. 'In those places where the monks stay for a long time on their knees, make sure that the floor is not in stone,' the abbot's brief asked. If there were any stained glass windows, 'there should be no colour, according to our tradition'. In the library, the brief asked for 'doors that don't slam, and a floor that mustn't creak'.

In the dormitory, there should be 'a cubicle for each monk, closed by a curtain, with a special snorers' section 'for about a quarter of the total'. They take the form of white cubes.

While the communists ruled Czechoslovakia, religion was officially discouraged. Churches were closed, monasteries dissolved, Catholic priests forced underground. There was no chance for any new monks to take their vows. After the end of communism, a handful of young men who believed that they had a religious calling were finally able to follow their vocation, travelling to France to be accepted as novitiates. When enough of them became full members of the Cistercian order, plans were made for them to start their own monastery in their homeland. It's only now, 15 years after the Velvet Revolution, that their plans have been realised.

Once a Cistercian monk has taken his vows, the monastery becomes his entire world, and Pawson spent time in Novy Dvur's mother house in France at Sept-Fons to get as close to this very particular way of life as he could.

I went with him on one visit. The food was good, served with wine and home-baked bread. You were welcome to join the services that are compulsory for the monks and take place throughout the day and night every four hours. It made me think of the constantly sleepless early days of parenthood. It's an experience that, whatever the extent of your own faith, quickly starts to have a profound effect on you. Your sense of time stops and somehow speeds up all at the same time. It clears your mind; ritual expands to fill every available synapse.

Last month I was in Novy Dvur to see the results of Pawson's research and to attend the consecration. It is perhaps the most unlikely place in the world to find the man who designed the store on Madison Avenue. But given that Pawson became famous for designing houses for the rich that look as austere as monasteries, there is a certain logic to the situation. Pawson, who has always wanted to live in the simplicity of a monk's cell, has finally had the chance to design a real one for himself.

Like the Cistercians, Pawson rejects ornamentalism. He looks for spiritual qualities in light and space.

At the heart of the monastery is a modest old baroque manor house which forms the starting point for an extraordinary series of new buildings to sustain the community of 40 or so monks who will spend the rest of their lives here. There is a beautiful new church that manages to be both austere in its form and also a space with the quality of richness. The monks have a workshop in which they make mustard to raise funds to help support themselves. There is a small wood-fired generator, as well as the dormitory in which they sleep, and the refectory where they eat in silence.

I watch as holy water is splashed vigorously on the white plaster walls of the monastery. The relics that will bestow sanctity on them have come all the way from Novy Dvur's Burgundian mother house in a golden ark protected by a purple cloth. Four monks, also dressed in purple, have hoisted it up on their shoulders on stout timber staves, and carried it carefully around the perimeter according to Cistercian ritual. You can hear the sound of chanting in the distance and the tolling of the occasional bell. The scent of pine trees floats across the wide Bohemian landscape mingling with a hint of incense.

But Novy Dvur, impossibly remote though it is, still hasn't quite settled down to the Cistercian rule of silence and seclusion from the world. The Mass that the local bishop is conducting is being relayed on giant screens to a crowd several thousand strong in the surrounding fields. The courtyard in the cloister will never look like this again. It is full of people who, once the consecration is over, won't be allowed back by a closed order that discourages visitors and forbids women altogether.

If elderly Czechs can still dimly remember what is expected of the pious, to judge by the celebrations at Novy Dvur, the younger generation is still trying to get the hang of it. A very young nun sprawls flirtatiously on the lawn in the cloister. She talks animatedly to a lolling, ponytailed figure with a beard whom I initially take to be a goth. When he rises to stand, he turns out to be a monk. And the ranks of the clergy are matched by rows of architects in their own priestly all-black uniforms, drawn by the chance to see Pawson's largest work to date.

The crowds are full of old men in berets, their faces like crags. There are stooped peasant women in floral print starched aprons. Soviet-era fashion still marks out their urban sisters, who sport ankle socks or rolled-down nylons. But there are also young men in black dusters and cowboy hats. Is it the deep-seated sense of gloom that comes so naturally to the Czechs that makes them such avid country and western fans?

'In those places where the monks stay for a long time on their knees, make sure that the floor is not in stone,' the abbot's brief asked.

Pawson has designed the monastery to be a home. The monks' cells are sparse cubicles, with just a few hooks and open shelves for their possessions. But the monastery been freed from the distractions and petty nuisances of noise and cramped conditions that would make the monks' lives even more difficult. It's where they pray, where they contemplate their spiritual existence and look forward to the next world. The infirmary, where the younger monks care for those members of the community too frail to manage, has windows that overlook the cemetery.

Pawson's architecture is a narrative of the life of the community, with the church altar hiding a cascade of steps that leads down to the cemetery. The Cistercians have always treated architecture as a reflection of their principles of simplicity and self denial. In the early days they produced buildings of sublime beauty, such as the Romanesque abbey of Le Thoronet in Provence which has always been one of Pawson's own inspirations. He has tried to bring a sense of that quality to Novy Dvur�'something that is new, but true to the Cistercian essence', as he puts it.

It's a conundrum that has exercised the Catholic establishment throughout the 20th century. Troubled that the church was losing ground because its art and architecture had started to look out of touch, Paul Valliant, an intellectual in the French church, was responsible for Matisse's chapel at St Paul de Vence and secured two major religious commissions for Le Corbusier.

Pawson has worked in a very different context, but lives up to those ambitions. Like the Cistercians, he rejects ornamentalism. He looks for spiritual qualities in light and space. He has ranged his buildings in a rectangular cloister around a sloping garden courtyard; they integrate themselves with the restored manor house that forms one side of it, but transform its meaning. The cloister is all glass and provides views across the courtyard and, at the end of the long corridors, a glimpse of the landscape beyond. For Pawson, who has until now worked mostly at the scale of the domestic house, it is a profound and impressive demonstration of his abilities with a much larger scope.

The ranks of the clergy are matched by rows of architects in their own priestly all-black uniforms, drawn by the chance to see Pawson's largest work to date.

As the Mass comes to an end, the white-clad monks come out of the church to take Communion with the crowds. Snaking lines build up for the wafer and the blessing. There is a picnic after the Mass, with vats of goulash, trays of doughnuts, wine, sausages, beer and ice cream. I have never seen so many monks gathered together in one place. There are monks with bad haircuts, burly monks who haven't shaved, thin monks, trainee monks, more young monks than anyone has seen for a very long time, here to celebrate the consecration of their colleagues' monastery.

There are monks from France, black monks (a few, anyway), monks with their hair cropped tight to their scalps, monks with eccentric tonsures wrapped around the edges of their heads in tufts.

After the picnic a procession of them forms to wind their way around the monastery, past the neatly restored walls of the old manor house, down to the bottom of the hill, past the mustard factory and the cemetery. The artist Michael Craig-Martin, standing in the crowd to watch, feels his Benedictine schooldays come flooding back. Paul Smith is standing outside the church taking photographs. Inside, the white walls float like blades above the heads of the congregation. A gothic carved figure of the Virgin sits on a totem behind the altar. And the monks smile beatifically as they begin to chant.