The canyon walls rise steeply on either side of the Colorado River, their sheer sides revealing the violent mysteries of the formation of the earth's crust. A mile beneath the jagged rim of the Grand Canyon, two large inflatable rubber rafts drift with the slow current of the waterway. The fourteen people aboard each raft listen intently for a change in the voice of the river. From the near deafening quiet a mere half hour before, there is now a subtle note of urgency. A muted rumbling increases as the surface of the river becomes deceptively calm; stretched smooth by the quickening of the current ahead. The noise becomes a roaring crescendo and the boatman seated at the back of the raft calls the long-awaited order.

"Rapids position!" and the fourteen passengers break into a flurry of activity. Cameras are thrust deep into waterproof cases, hats and spectacles are fastened tightly, everybody obediently assumes their positions on the raft's deck with a secure hold on the guy ropes.

Suddenly the leading raft seems to shudder and drop. For a moment only the heads and shoulders of its passengers are visible from behind, then they too disappear. On the second raft there is little time for anticipation before it also pitches forward into a boiling stairwell of huge, crashing waves. Walls of white water break over the twisting, buckling pontoons of the raft, driving it under the turbulence.

Moments later it bursts through the surface, its passengers drenched and spluttering, only to collide with another wave in mid-air before continuing on a roller-coaster ride through the fierce rapids. It's just as well the superbly designed raft has everything that could possibly move firmly secured, for the impact of the raging waters would certainly have claimed any cargo that was not properly fastened, including the passengers.

The cauldron of the rapids is left behind and a cheer goes up for the boatmen who has so ably steered the large inflatable through the challenge of the wild waters. Passengers, drenched to the skin, laugh and chatter, shaking the water from their hair. With the air so dry at the bottom of the Grand Canyon, they will be dry in minutes.

We are on a nine-day 'Grand Canyon Expeditions' raft trip down one of the several natural wonders of the world. The rapids of the Colorado River provide real adventure in its truest form. This whole journey explores in detail an area of incredible beauty with a heady mix of both excitement and serenity. Cut off from all outside contact and communication, our boatman will guide us for 280 miles along ever-changing vistas.

Discovered by the Spaniard Lopez de Cardenas in 1540 when on an expedition to find the legendary gold-laden Seven Cities of Cibola, the Grand Canyon was considered impassable till 1826. The Colorado River at the canyon's base defied the brave and foolhardy who tried to navigate its dangerous waters until 1869, when Major John Powell, a one-armed veteran of the American Civil War's famed Battle of Shiloh, led an expedition of ten men to fathom its mysteries from which only three would survive.

In the 280 miles between Lee's Ferry and Lake Mead, there are only three or four places that are reasonably accessible from the rim of the Canyon. The National Parks Service that controls the Colorado and its river traffic is responsible for limiting the numbers of people travelling on the river and to make sure that no ecological damage is inflicted upon this marvel of nature.

They achieve this by meticulously controlling the operators of the river trips and carefully screening individuals and groups of boaters, rafters and kayakers - so much so, that the latter may have to wait seven years from their first application before being granted permission to take the trip and then only if they have renewed their application every year in the interim. For the lucky few who are granted the opportunity, the journey will be one of the great adventures of their lives.

The first surprise will be the sort of fellow passenger you will meet. On other white-water rafting trips you might experience a round the world, you might expect that your fellow passengers will be 'Tarzan and Jane' types in their twenties and thirties and almost always fervent outdoor enthusiasts. On the Colorado trips, however, many of the participants are an unexpected range of business people with an average age of around 40 years. Our group held a curious mix of city-dwelling professionals: lawyers, teachers, nurses, computer specialists, university professors and engineers amongst other seemingly incongruous career people. It goes without saying that all harboured a love of adventure and were reasonably fit. On this rafting cruise there is no rowing involved - an outboard motor powers and steers the craft.

At first somewhat shy of each other, the group became a team within a mere two or three days and firm friendships evolved which are likely to last many years. You soon find that different people have different reasons for taking the trip. For some it is an opportunity to escape the pressures of work and day-to-day responsibilities, for others the drawcard is the magic of the Canyon itself and the communion with nature in absolute seclusion. Lying in one's sleeping-bag and looking up at the myriad of stars twinkling in an ink-blue sky, with the blackness of the canyon walls looming up on either side and rapids gurgling in the distance - it is simply an experience that will prove unforgettable in one's lifetime.

Still others make the trip for photography, for archaeology, for studying natural history, or simply to observe the unique environment of the river. Then there are those who take the nine days to have time to think - to reflect on their lives and to place problems into a perspective that they cannot possibly achieve in the pressurised world of the city.

The 'Grand Canyon Expeditions' company run what most people in the industry consider to be the best of the 'River Runners', and are masterful at stashing the boat with every conceivable necessity. Each day's meals are pre-organised and the ingredients are cleverly stowed in waterproof compartments so that they are easily accessible. With two rafts travelling together, one is set up as the 'lunch boat', the other the 'dinner boat', simplifying access and planning for meals. Everything carried on board is neatly stowed again after use.

The National Parks Service and the boat operators themselves must ensure that every scrap of waste, every cigarette butt, every can and bottle and even the ash from campfires is carried out of the canyon. With an almost zero rainfall and the dry air in this area, nothing decomposes and whatever is left behind will remain there virtually forever, so extreme care must be taken. Chemical toilets are carried on the rafts as is firewood which is burnt each night on a special metal plate, and the ash packed and restowed onto the raft in the morning.

A typical day on the river starts at about 6.30 a.m. When we rise the Canyon is still relatively dark at the campsite, but the tops of the peaks around the rim are already bathed in the golden glow of morning sunlight and the aroma of freshly brewed coffee is drifting across the still air. By 7.00 a.m. our versatile boatmen and their helpers have prepared a delicious breakfast of eggs, sausages, fruit juice and muffins. Sleeping bags are rolled up and the river bags repacked. The courageous have a quick dip in the river - the 10 degrees celsius temperature being an incentive for brevity. Most men grow beards but a few stalwarts shave, and by 8.30 a.m. everything is loaded onto the rafts and the day's journey begins as the sunlight begins to stream into corners of the Canyon.

As we float down the river through some minor rapids, the scenery is breathtaking: jagged peaks and vertical walls alternate textures and colours. Grey granite changes to black lava and then soft pink sandstone. Sandy beaches occasionally appear along the river and from time to time you come across lush oases, where water seeps down canyon walls through geological faultlines. We tie up at these beaches to hike up the valley to ruins of dwellings, several hundred years old, once inhabited by the Indian tribes that lived along this section of the Colorado.

Another small canyon which intersects the river ahead is Vasey's Paradise, where water gushes from the Canyon's walls. Here wildflowers, moss and ferns provide a lush green that seems strangely out of place in this desert setting. We stop to fill containers of drinking water from the waterfall, an experience that will substitute for showers almost every day.

At lunchtime our rafts stop at Redwall Cavern, a huge natural cave big enough to hold 5,000 people. Shaped like an auditorium with a sand floor, this vast cave is one of the wonders of the canyon trip. Lunch consists of sandwiches with the ample fillings set out on a metal tray from which fellow rafters select their own combinations. Cans of soft drink are available from the raft at all times.

Leaving the cavern we drift further down the river and our boatman-guide regales us with fascinating stories of early explorers who lost their lives in these very rapids. We tie up again for another canyon walk, followed by a cold beer on our return to the raft. The sun is strong but an effective sunscreen ensures that there are no problems. Setting off again, we spot herons on the river banks and eagles circling in the distance.

By 6.00 p.m. we have reached our next campsite. While we prepare our sleeping bags, have a quick swim and set up camp for the night, the boat crews unpack the camp ovens and prepare a sumptuous meal of steak, dutch-oven potatoes, green salad and, to our surprise, even bake fresh cakes.

Some enthusiastic anglers fish. Trout are so abundant in the early sections of the river before it gets muddy that enough fish, up to 2 kg in size, are caught for everyone's breakfast the next morning. After dinner, we sit around the campfire exchanging stories and cementing friendships in the process. Unlimited supplies of coffee, tea and cask wines are available but the numbers thin as one by one we head exhaustedly for our sleeping bags.

I look up at the stars. Not since childhood can I remember a sky so clear and the Milky Way so brilliant. From time to time planes cross over the canyon, for this is the major aircraft route between Los Angeles and Las Vegas. At other times I see a tiny silver dot, the size of the smallest star, pass across the sky, but one of the many satellites that would be invisible were the night not so clear. My stargazing lasts no more than five minutes - sleep on this trip is easy, even for the most hardened insomniac.

Only 1600 people are permitted to take the river run down the Colorado each year: I am delighted that I have had the privilege to be one of them.