From political leaders to literary giants, an open canoe trip is the thinking man's adventure. But as Rob Penn found on Scotland's waters, even a gentle paddle requires more than just brainpower

"Many pioneers in environmentalism and the philo-sophy of the outdoors have been keen canoeists," he adds, as we haul the kitbags down to the loch's edge.

This is an inspiring preamble to our trip - a three-day open canoeing and walking journey into the autumn wilderness of Assynt in North-west Scotland. On the train to Inverness, I had been anticipating a bruising physical encounter. But, easing across the first loch, I wonder if I am actually set for several days of idle contemplation, sitting in the front of the canoe, thinking great thoughts and experiencing inner renewal. Then the first squall strikes.

I see it initially, whistling across the loch towards us, tearing the ink-black water up into white caps and twizzles of spray. Then I hear it: a great moaning. Finally, I can feel it.

"Brace!" Jamie shouts. A rubbery gust thumps the side of the canoe. Waves breach the bow and shower me with icy water. My knuckles go white. Even Jamie, who has the shoulders of a prize Angus bull, is struggling. After five, deltoid-burning minutes, we have not moved a metre. I am exhausted when Jamie finally hoists the white flag and steers us to shore.

"Do you remember Billy Connolly's maxim?," he asks, dragging the canoe to safety on the rocks. "If you don't like the weather in Scotland, you only have to wait around for 20 minutes before it changes. Shall we have a cup of tea?"

There is nothing so impermanent as the sky that lours over this remarkable landscape - the weather tears straight off the Minch channel, dragging an ever-changing canopy overhead. Half an hour later, as predicted, we are stroking our way lazily in and out of pools of sunlight, across the middle of Loch Sionascaig, past islands of sprouting juniper and birch, between the towering, isolated peaks of Coigach and Assynt.

Now that our passage is easier, Jamie starts to work on my technique. Paddling an open canoe is actually more technical than it first appears, and in those minutes of extremis, I had been exposed. There are over 30 named strokes, Jamie explains, "but you only need half a dozen at this stage".

The key to efficient solo paddling is the J-stroke, a forward paddle, used in the stern, that finishes with the blade angled away from the canoe, making a letter 'J'. It is used to make the canoe go in a straight line when paddling solo. More advanced paddlers can opt for the Indian stroke, a variation of the J, where the grip of the paddle is rotated in the hand to move the blade back through the water for the next stroke. It's a handy skill to master in strong winds, and as there is no sound from the paddle, it is good for viewing wildlife.

With Jamie powering away in the stern, I only really need to master the goon stroke (a basic forward paddle) and the bow-rudder stroke, holding the blade still in the water and using the momentum of the boat to steer us away from boulders lurking just below the surface at the loch's edge.

More squalls come and go. In between them, I begin to appreciate how this could be a source of spiritual enrichment and the sport of the thinking outdoorsman. Jamie, who works as an environmental lawyer and is well versed in wilderness advocacy, tells me more about his paddling heroes: John Muir, the tough Scot who essentially founded the conservation movement in the US around the beginning of the 20th century, made several journeys by canoe; Henry David Thoreau, the backwoods philosopher who wrote his first book about a canoe journey, and who penned the haunting words: "The mass of men lead lives of quiet desperation" in his classic wilderness book, Walden; and Aldo Leopold, the father of wildlife ecology, who was was also happiest with a paddle in his hands.

More recently, that well-known professional outdoorsman Ray Mears extolled the virtues of a hand-built, birch-bark canoe in the BBC series Bushcraft Survival. Open canoeing is undoubtedly elemental. This was, perhaps, best expressed by Pierre Elliott Trudeau, the former Canadian prime minister: what sets a canoeing expedition apart is that it purifies you more rapidly and inescapably than any other, he said. Travel a thousand miles by train and you are a brute; pedal five hundred on a bicycle and you remain basically a bourgeois; paddle a hundred in a canoe and you are already a child of nature.

When we reach the end of Loch Sionascaig, we have paddled two miles. I presume this is as far as the canoe goes, but I have not yet heard of portage. This is where the open canoe comes into its own: we rope up and drag the canoe over a low bridge of land covered in heather. Ten minutes later, we are off again across Loch Gainmheich, heading deeper into one of Britain's few remaining empty quarters.

"The canoe really works up here," Jamie says as we reach our campsite, a sandy beach beneath the sandstone cliffs of the 849-metre Col Mur. You can paddle and portage your way into the heart of this wilderness area, where there are dozens of small lochs, divided only by slim bridges of land.

You could walk in, of course, but the difference with a canoe is that you can easily bring all you need for a great trip. This is music to my ears, since the canoeing has induced a voracious hunger. By the time I have my tent up and the evening light has paled away to a smudge of pink on the western horizon, Jamie has cooked a three-course dinner. We eat beside a driftwood fire and wash broth, burritos and flapjack down with a peaty dram.

Breakfast is no less of a gourmet experience. Over fruit, muesli, milk and croissants I confess that I feel like I have been sharing the responsibilities of Atlas.

"Good job we're walking today, then," Jamie says smiling, "so you can rest your shoulders and give the legs a workout." And with a 360-degree sweep of his hand, he asks: "Which one of these beauties do you fancy climbing?"

Cul Mor, Stac Pollaidh, Cul Beag, Suilven and Ben Mor Coigach - these are the fantastic Torridonian sandstone peaks that dominate the extraordinary cnoc-and-lochan (from the Gaelic words for hill and small lake) landscape north of Ullapool. Like a carefully hung art exhibition, each mountain - the "Celtic Sphinxes" someone called them - has its own brooding outline and space.

We set off for the top of Cul Beag (769m) via the flanks of Cul Mor, where we spot a herd of 70 or so hind, partly camouflaged in the turning bracken beneath the fretted buttresses of rock. I am no geologist, but it is impossible to ignore the imprint of glaciation here.

We drop down to cross Glen Laoigh, then we are climbing hard again over knurled hills of gneiss - coarse-grained rock - and on to the sandstone heights. I feel like every sinew in my body has done its duty when we gain the top of Cul Beag. Clouds are swirling all around us and, applying the Billy Connolly rule again, we crouch in the lee of the cairn and have a mug of tea.

We can only sense the sunshine at first, and then it bursts through in a glory of golden pools out on the Atlantic, illuminating the Summer Isles. Knockan crag and the weathered, tor-like crown of Stac Pollaidh catch early glints.

Blown on by a crisp south-westerly wind, the clouds finally clear, revealing the landscape in all its russet-and-grey glory. We have a bird's-eye view of the whole area and, to make the point, a pair of golden eagles, racing downwind on stiffened wings, pass 100 metres below us.

With my eye, I trace our route back away from the summit - down the mountain and over the glen, past the campsite, across the lochs and the portages - to where we started. In the far distance, and out of sight, is the car. It will take us a day and a half to get back there, and it is a journey that can wait.

How to find peace and quiet in the Highlands

Wilderness Scotland (0131 625 6635, offer canoeing and walking trips in the lochs, rivers and mountains of the North-West Highlands. Prices from £475 per person, all-inclusive, for a maximum of eight people. Trips start and finish in Inverness, and other open canoe itineraries are available, including a descent of the River Spey. First ScotRail's Caledonian Sleeper service (08457 55 00 33, runs between London and Inverness six nights a week (not Saturdays). Bargain Berth fares start at £19 one way but must be booked online; Standard Apex returns cost from £89 and first class from £190.