Yin, yang and Yen

When the founder of an obscure aesthetic sect wanted a place to put her tea utensils, she called IM Pei. He built her a museum. Fiona Sturges went to see it in Japan

IM PEI likes to tell a story about his latest building, a museum housing an extensive collection of Eastern antiquities in a remote Japanese mountain range. "As soon as I saw the site I remembered a poem that I was told as a child, called 'The Tale of the Peach Blossom Spring', about a fisherman who after a long journey discovers the valley of a lost paradise through a cave opening. The Miho Museum has the same qualities of an unfolding journey, bringing with it a sense of discovery. I see it as a kind of Shangri-La." The Chinese-American architect of the Louvre pyramid claims that he had no idea that the valley beyond the museum was called Peach Blossom Valley until well after the plans were laid.

The Miho Museum teeters on a mapled mountain top by Shigaraki, a small town north-east of Kyoto. Its location serves as a perfect vantage point for an earlier Pei creation, a bell tower shaped like a stringed musical instrument. Both were were commissioned by Mihoko Koyama, one of the richest women in Japan.

In 1941, Mihoko Koyama met the spiritual philosopher Mokichi Okada (1882-1955). She decided to devote her life to the practice of his teaching and, in 1970, founded the Shinji Shumeikai group, a "spiritual organisation" dedicated to the "pursuit of truth, virtue and beauty". The group's secular philosophy is realised by the collection, preservation and public exhibition of works of art.

The Shinji Shumeikai established a "sanctuary" near Shigaraki. In 1989, Pei was invited to create the bell tower as a monument to the obscure sect. A few years later, Koyama was looking for a home for her small collection of Japanese tea-ceremony objects, aquired over 40 years and donated to the Shumeikai. She was so delighted with Pei's bell tower that she asked him to design a museum for the tea utensils. Pei agreed, with one condition: that Koyama and the sect extend their collection, to make it more appealing to an international audience. They accepted his demand without question, only specifying that he should build the museum in view of their sacred bell tower. Pei was more than happy to oblige.

The site, though spectacular, posed several problems, not least how to get to it. The area is a nature reserve so there were numerous prefectural regulations about what could and could not be done to the landscape. Undaunted by these obstacles, the Shinji Shumeikai simply bought the adjoining ridge, enabling Pei to plough a tunnel through it in order to reach the intended site. The result is stunning.

While engineers hacked away at the mountainside, Mihoko Koyama and her daughter, Hiroko, went on a monumental shopping spree, funded partly by the Shumei Culture Foundation, the administering body of the museum, and by voluntary donations from members of the Shumeikai. Koyama senior is the heiress of a multi-million pound textiles company.

Where many Western institutions find themselves selling off their treasures simply to maintain their buildings, the Koyamas had the art world at their feet. They soon found themselves inundated with offers from dealers across the globe. Since every bogus art dealer everywhere was by now on full alert, the Koyamas hired a host of experts to assist them with their spending and check on the authenticity of the articles. It proved a lucrative situation for art magnate Noriyoshi Horiuchi, owner of galleries both in London and Tokyo. On hearing of the Koyamas' predicament he sought out the finest objects on the market on their behalf. It was the beginning of a partnership which lasted six years and yielded approximately 1,000 objects of ancient Egyptian, West and South Asian, Chinese, Korean and Persian antiquity. They are said to be worth in excess of pounds 150 million.

One of the works of art hit the spotlight in Britain in 1994 when it was sold at Christies for pounds 7,701,500. The limestone Assyrian carving of a winged and bearded "genius", flanked by royal attendants, was uncovered in a school tuck-shop in Canford, Dorset, having previously been plastered over and used as a dartboard by students. Controversy arose at the sale when the carving, originally excavated from the lost city of Nimrud, Northern Iraq, was claimed by the Iraqi government who demanded, unsuccessfully, that the sale be stopped.

Hiroko Koyama is modest about her and her mother's acquisitions. "I feel it is extraordinary that this happened, it really is a miracle. When IM Pei asked that the collection become more international we were clueless about where to turn - we certainly didn't want to buy things just for the sake of filling up the museum. But then we met Mr Horiuchi who showed us some photos of some beautiful objects and we just fell in love with them."

Initially, Pei planned quite a small building, but as the collection grew, so did the museum. Even Pei could not anticipate quite the extent of the Shinji Shumeikai's resources: "I did not realise at what pace the plan would have to be revised. We were able to accommodate this need for expansion by digging underground. It was a bit of an ad hoc exercise in the end." As a result, 80 per cent of the building now lies underground and unless viewed from the air, its vast scale is not apparent. The total cost, to date, is 25 billion Yen, or $215m.

The museum is reached through the ridge: a wide, ceramic suspension bridge emerges from a dimly lit silver tunnel, supported by a fan of cables. The bridge itself is straddled by a giant arch that Pei proudly tells us took three months to weld. It's an approach so bold that at first glimpse the building is a bit of a disappointment - its timid terraces fade into the shadow of such hi-tech handiwork.

Unlike most new Japanese buildings, which look resolutely to the future, Pei's building is designed to integrate with its sensational surroundings and revel, as the collection does, in Japanese tradition. As an architect brought up in the United States, Pei believes he is more in touch with Japan's historical roots that some of his homeland's own architects. "You cannot arbitrarily start something and hope it will take root," he has said.

But for all its deference to Japanese heritage, the Miho building is distinctly recognisably Pei - Pei as in pyramid. Again, he has worked with a geometrical design, plotting a structure on a sharp, isosceles grid - which, here, perfectly mirrors the peaks and valleys of the mountains. In the entrance hall, variable triangles rise up towards giant skylights which are divided by heavy, tubular mullions. "The entrance hall displays a variation of a very simple theme," explains Pei excitedly. "I like to think that this variation can be infinite." The stark drama of these skylights is diluted by their faux-bamboo blinds. Wood is a key material of ancient Japanese architecture, so Pei naturally wanted to use it here. But in the middle of a steel and glass structure, it would probably have warped. He found a solution in aluminium slats, styled and coloured to look like wood. The result is a qualified success: the hall has the feel of a Swiss chalet, but the wooden effect, in combination with the honey-coloured marble floor tiles, brings a warmth to the interior that marks a step away from the clinical minimalism of Western art spaces.

One of the most striking features of the Miho is the exquisite finish of its interior, so glossy it leads one to suspect that the Shumeikai minions must be furtively buffing and polishing the surfaces every time one's back is turned. Every square inch is pristine, from the tessellated tiles in the hallway to the perfectly moulded joints linking the many panes of glass - 106 different types, in fact. The labyrinthine corridors and little galleries seem endless - "the pleasure being in the journey, not the destination," as Pei exclaims, reminded of his poem.

The collection is displayed with equal attention to detail. Great pains have been taken to ensure that each object is as important as the next. Each has its own individual seismically-safe mount and extraordinarily advanced lighting design - yet another aspect of the project with which the architect has enthusiastically concerned himself.

Despite the Shumeikai's extravagant pledge to share their vision of beauty with the world, their museum is pretty difficult to reach. Even in good weather, the long, wiggly road up the Shigaraki mountainside is hair- raising; in winter, ice and snow make the road impassable. So the museum will be shut between December and March. Only the very seasoned traveller would brave the trek for a dose of soul-cleansing, though stories of strange cults, mystical journeys and hidden treasures may be the incentive the Western art lover needs to assuage millennial angst and make the spiritual-aesthetic pilgrimage to the East.

Miho Museum, Shigaraki, Shiga 529-18, Japan (00 81 748 82 3414), open Mar to Nov.