Twenty-seven hours into the world's toughest footrace, things really started to get interesting. The physical agony I'd been prepared for; the mental torment came out of the blue. Or rather the black. Running up a steep forest path at midnight, my head-torch began picking out writhing, reptilian forms, menacing faces and ... cartoon characters.

Shuffling up the hill ahead of me, a fellow competitor was performing comical double takes, clearly also hallucinating. As I neared, his roving spotlight illuminated a squat bush to our left and, as one, we leapt the other way. Sitting there, his coat a vivid blue but otherwise unmistakable, was Pluto. Welcome to the mad, mad world of the Ultra-Trail du Mont Blanc.

Is it really the world's toughest footrace? This annual orgy of masochism certainly takes some beating. The course, a three-country circumnavigation of the massif dominated by Europe's highest mountain, is 103 miles long with an aggregate climb of 30,839ft. Put another way, you're running non-stop from London to Birmingham via the cruising altitude of a jumbo jet. Throw in chronic sleep deprivation and a temperature range of -10C to 30C, and you have an event that is probably going to sting a bit.

So, why do it? To paraphrase Lance Armstrong, it wasn't about the running. Neither myself nor Blake and Cal, the two friends who'd initiated this lunacy, were runners in the strictest sense. That is, we'd never discussed split-times. Or worn Lycra unless absolutely necessary. But driven by the same ill-defined, thirtysomething challenge lust that was to take us to the Alps, we'd completed various marathons and multi-stage events, accruing sufficient points to enter the UTMB.

A festival atmosphere greeted us in Chamonix, the start and finish point. In its seventh year, the event is already huge, dominating the final weekend of August. Lean, weathered competitors roamed the town, sporting elaborate equipment, loading up on specialist fuel. We felt like impostors. This was the pinnacle of distance running; most of our kit still had the price tags on.

Seemingly the entire community converged on the town square to cheer us off on the Friday evening - 2,600 runners outnumbered tenfold by a raucous, cowbell-jangling multitude. The fervour seemed proportional to what awaited, making my stomach churn. To the stirring strains of Vangelis, we were off.

The first few miles were flat, well-supported and fun, but no one was buying it. Sure enough, the first climb wasn't far off. Our training for the event had been improvised at best: Cal had focused on core strength; myself on wearing a groove into a single hill in Greenwich Park; Blake on trying to give up smoking. We certainly could have done more. But as we toiled to the top of La Charme in the gathering gloom, it became apparent that nothing would have adequately prepared us. This was an exam without a syllabus.