By the time you read this, 2,400 teenagers will be slogging across up to 55 miles of England's most rugged terrain, scrambling up ten granite outcrops, and generally making themselves very wet and tired. Why? Because, as Mallory said of Everest, it is there.

Yes, it's the Ten Tors: the army-organised weekend that challenges 400 teams of schoolchildren to find their way from hill to hill across Dartmoor. To do the Ten Tors is one of the great rites of passage for intrepid youngsters. And it's by no means certain that they will all complete the two-day hike.

Last year the event was abandoned after one day because torrential rain had turned rivers into torrents (the organisers were, of course, very aware that a 14-year-old girl had drowned while training for the event). Two years earlier the thermometer hit 78F and many entrants were treated for dehydration. On Dartmoor nothing is predictable. In this timid age when we wrap kids in cotton-wool and fret about them taking the bus to school, thank goodness that events like the Ten Tors haven't yet been banned.

Even in a country as supposedly “tame” as Britain, there are still dozens of daunting outdoor treks that attract thousands of determined masochists every year. I am a mere dilettante in this field, especially when compared with the fell-runners who whizz over our biggest hills at unbelievable speeds. It took me eight hours, for instance, to get up and down the three great Yorkshire Peaks (Pen-y-Ghent, Whernside and Ingleborough) that some sickeningly fit Glaswegian has just conquered in two hours and 53 minutes. But I have twice completed British rambling's equivalent to Chairman Mao's Long March - the infamous Lyke Wake Walk, a 42-mile slog across the boggy North York Moors, where the Emperor Hadrian reputedly lost an entire legion of his army. If you see a lot of Italian blokes in short skirts and plumed helmets, do let him know.

And I've also done the British Three Peaks - a mad challenge that commits you to climbing to the highest points in Scotland, England and Wales inside 24 hours. Scrambling up and down Ben Nevis, Scafell Pike and Snowdon is bad enough. The real nightmare, though, is getting through the traffic on the M6.

But there are so many other legendary challenges out there, and so few years left before my creaky old knees finally scream “you cannot be serious!” In Scotland, for instance, I've climbed just three Munros (hills of 3,000ft and upwards) out of a possible 269. Some people have “bagged” them all. And I've yet to attempt the jolly-sounding Four Inns Walk in the Peak District - though my enthusiasm for that has cooled slightly since learning that it involves 45 miles of very hard walking, and that one of the pubs is shut anyway.

We bang on so much about preserving our countryside. But most of the time we observe it through a car or train window. Believe me, the best bits can only be reached on foot. If you've never tried, buy a pair of decent boots and some sturdy waterproofs, and get trudging. You'll be amazed at how much fun it is - at least when you stop for a breather.