This pruning or bowdlerisation is risky. The fearsome deity, Fudo Myo-o is not one to trifle with. As with so many gods, his habitat is not the lowlands but the mountain peak. He is lord of many calamities – war, earthquake, epidemics, traffic accidents, and above all, destructive fire. He also handles astrology, trees, bothersome demons and waterfalls, but fire is his major concern. The Goma rites were devised 12 centuries ago to turn away possible divine wrath and ensure protection for the coming year. Celebrated in deep winter, the rites petition for good crops, no floods, no devastating fires. If they are correctly performed Fudo Myo-o will speak to the people by medium.

Thus far, except for the medium, the description of the ceremonies could apply to most Christian Christmas services. But Goma also has Yamabushi monks of an ascetic, profoundly devout order attached to the Shingon sect. Officially Buddhist, these strange religious, whether shamanistic or saintly, include in their spectrum of faith elements from Shinto and Tendai, the latter a severe discipline that produced the terrible warrior monks of Japanese history.

As I lived near many Shingon temples in the Higashiyama region, a spectacular tumble of mountains and streams east of Kyoto, I had twice witnessed the fire ceremonies, both times in the evening. Now I wanted to watch in daylight. As well, I thought that the spirit of Fudo Myo-o might come upon me, and I would find the nerve to do some firewalking myself. (I didn't really believe this.)

So, early on a bright, unspeakably cold late December morning, there I was halfway up a mountain and, as far as I could see, the only gaijin in a 2000-strong crowd of anticipatory devotees. Through the aisles of cryptomeria, where mist still hovered, I could see the thatched roofs of the faraway temple, clinging in steps and stairs to the mountain as though it were itself a graceful outcrop.

It was not easy getting there. For 45 minutes we climbed a stairway of a path and then 100 stone steps going straight up like a ladder. There must have been some merit in the actual climb because I saw a young father most tenderly helping his tiny boy to jump from step to step up that backbreaking ascent. He was really swinging the child from step to step, allowing the little one's feet to touch each one.

All the time the inward-pressing trees, the hidden gorges, the cold air itself echoed with what seemed to be the cries of humpback whales, lonely and lost. What an extraordinary sound is that of the conch shell trumpet! It can arrest you in mid-step; the visions it brings to mind are never human.

An old man trudged beside me. I said, "I hear the Yamabushi." He was so pleased to find a gaijin with some slight knowledge that he dug in the pack he carried and produced a bean paste bun. This he wrapped in a Kleenex and presented with approving smiles and bows.

Many of the climbers were old women, some in the white clothing of pilgrims, happy all, encouraging each other with drawling chirrups. We came out at last into a clearing, a terrace levelled amidst the hanging forest, a mere ledge in that immensity. On one side precipitous pinnacled rocks rose out of dirty snow. Squeezed in a crevice, a tiny maple showed a blush of leaves, the last of the year. This delighted many of the pilgrims, and the little tree received bows and cries of congratulation. In the centre of the clearing, a tall pyre, fenced about with cypress boughs, awaited the blazing arrow that would kindle the skilfully stacked twigs and send the sacred smoke to Fudo in his high abode. Would the smoke ascend like a pillar, or would it sulk and choke everyone in breathing distance?

Already the atmosphere was tensely expectant. Far above in the temple someone softly touched a bronze gong. The crowd was so quiet I could hear the clucking of water running down an unseen pebbled channel.

Certainly the Yamabushi looked magnificent. Seeming taller and burlier than most Japanese, their air of command was unmistakable. Whenever one looked my way, I closed my eyes taking no chances with any person who has gained spiritual powers by means of inhuman austerities – standing under waterfalls for weeks at a time, climbing ladders of swords, fire-walking, vanquishing demons. Much of the time I believe in shamanism. The training has always been the same whether Greek, Persian or Amerindian. There seems to be no time in recorded history when men have not submitted themselves to bitter isolation, fasting, freezing, delta meditation for years, finally undergoing the deathly initiation sometimes called the descent into hell and emerging a person with otherworld powers.

Yet look at these Yamabushi in their fantastic array. Is this ceremonial garb the other side of asceticism? Are these explosive colours magical as well? The officiants wear immensely full white or cream breeches, tucked into leggings bound with black. An angular jacket or robe, with vast pleated sleeves, is ornamented front and back with four fat pompoms. The different colours of the pompoms probably indicate rank. I find it intriguing that they, and the vestments, are not in the Buddhist but the Shinto sacred colours, white, red, yellow, a curious brilliant blue-green and a shattering violet. It must be double-dyed, almost ultra-violet, disturbing to the eye. Each monk carries the traditional staff with six loose metal rings which, when shaken, warn unwary animals and insects out of his path. Yet for 20 minutes there is not a jingle.

Suddenly, out of nowhere, there comes a stab of flame through the air, cries of fright and wonder from the crowd, a thud and an almost instant roar and crackle. The pyre is alight, raging, a perfect bonfire; the onlookers shout with joy, and then, as if suddenly conscious that this is an occasion for reverence, fall quiet except for a waiting, excited murmur. And there rises the smoke, straight up into the clear sky, as it should do. Good fortune next year!

People dart forward to throw into the flames charms and amulets, and requests written on thin strips of wood. I have nothing to throw, so a kindly woman gives me one of hers and with many encouragements pushes me towards the bonfire. As I consign the supplication to the fire, hoping it is not a request for a quick trip to the Western Paradise, I catch a glimpse of a black hooded figure slipping between the trees carrying a bow. This is the archer. He looks for all the world like a ninja. He is, anyway, a shadow amongst shadows.

Already the Yamabushi have directed the people back to their places, and obediently they go. It is time for the god to speak to the people. He does not always do so. There is, consequently, a little restless feeling of anxiety. Now I see with surprise a female Yamabushi, an elderly woman in the same fantastic vestments as the men, though with a long skirt instead of breeches. She leads into the clearing a pitiable rag of a woman – pale, shaking with cold in a thin white cotton kimono. Her head is down on her chest, she seems to have no will or intention of her own, but is pulled this way and that like a doll. They settle her on the ground and begin to chant, the woman Yamabushi keeping time by striking with a small belled staff on a wooden drum.

I feel most uneasy. There is nothing innocent and communal about this. That dazed-looking woman is on her own. I can feel energy increasing in the atmosphere. Even the air seems warmer. People are nervous and restless. All at once the medium lets loose an unearthly screech that echoes all around and bangs in the ears. The chanting stops dead. Somehow centred on her fleshless buttocks she begins to swing her body in wide, improbable circles, faster and faster, then slumps shuddering over her feet. A huge rasping voice comes from the sky, the medium, the forest, anywhere. Somebody screams, somebody faints, I want to run.

During the previous fire ceremonies I had attended, nothing like this had occurred. There had been mediums, yes, who answered questions from the priests in a high monotone; one had been distressed and tearful. Looking about me now I see faces mesmerised, awestruck, even horrorstruck. The deafening male voice utters maybe 25 words then fades. There are, curiously, no echoes. Then comes joyful pandemonium. The message was good, glorious! All hopes are realised. As I learned later the god himself had not spoken: the mighty voice belonged to a famous general of the Heian period who was his spokesman.

Amongst those about me I can discern some expression of disbelief and even amusement. An obvious salaryman looks at me and shrugs. I shake my head and make a bewildered gesture. We are all aware, even those rural villagers who still call in Yamabushi to heal and exorcise, of the marvels achievable with microphone technology and amplification. Still, a shock is a shock, no matter how it can be explained.

A few minutes later a little murmuring procession passes me, the female Yama­bushi and four or five women pilgrims, half-carrying the reeling, lolling figure of the medium, her eyes rolled back, her thin kimono soaked with sweat. Her flat breasts are stuck to the cotton, so wet is it.

I knew then I could easily start shaking myself, so I went away quickly. Halfway down the mountain I realised I had entirely forgotten the firewalking and that probably I'd never have another chance to discover if I was game enough to do it.

But isn't that the story every time you try to throw yourself with open mind and open heart into another race's mysteries? Something gets in the way, your imagination, your own spiritual or mental programming, something. The best you can do is pick up a fragment here and there, treasure it, know that this is a small memento of a strange and wonderful country, and that's all you'll get.