A dynamic Peter Conchie cycled to Dunwich from dusk to dawn. But why?
The Dunwich Dynamo is a 120-mile overnight bicycle ride from Stratford in East London to Dunwich Heath on the Suffolk coast, a wonderfully pointless trip to a place that barely exists. What may once have been the most important city in East Anglia has slumped into the sea over the past 1,000 years, with churches, harbours and a royal hunting-ground all victims of savage coastal erosion. Legend has it that bells can be heard ringing beneath the sea when the weather is rough. It is a place meriting a fantastic voyage.

Unofficially, the Dunwich Dynamo began 10 years ago. The organiser, Patrick Field, would ride out overnight to see friends in the area when the roads were quiet, then go for a swim until the chip shop opened. Five years ago,Mosquito Bikes in Islington became sponsors and the first official ride was born.

The starting-point is Eastway Cycle Circuit in Stratford, East London, where mechanics first assess machines for roadworthiness - a mixed bunch of tandems, tricycles, and recumbence, mountain, racing and touring bikes. As the organisers stress, the Dynamo is not a race (welcome news for the Japanese chap on a Raleigh Shopper); start times are 8pm, 10pm and midnight. Last weekend I chose the earliest departure. Within a few miles the faster riders had pulled ahead as London imperceptibly changed from city to countryside. I climbed Chingford Hill with its pretty church, glimpsed the sunset over Waltham Forest and joined the slipstream of a tricycle through the dusk of Epping Forest.

Once darkness fell, the flashing red bike lights of the riders in front formed a reassuring chain of beacons - a scene reminiscent of the film Field of Dreams. Three official control-points-cum-feeding-stations divided the intimidating distance into manageable segments; I reached the first at 11pm, after 29 miles. Outside the brilliantly lit Leaden Roding village hall lay dozens of abandoned bikes.

Three cups of tea, two flapjacks, some fruit cake and an orange squash later, I repacked my panniers, clammy with dew, and cycled off into the night. Riders were given detailed instructions and an emergency phone number, while bright signs and home-made coffee-jar lanterns marked turnings. However, despite the glorious moon it was easy to get lost. I was glad to have made bike-buddies - a South African London taxi driver, an architect and a student.

The journey then took us deeper into Essex, cruising blindly through the night, silent except for the treacly hum of tyre on Tarmac, through High Roding, Great Dunmow and Finchingfield. In Castle Headingham, the last town in Essex, the Bell Inn was having a lock-in, with heartfelt singing echoing along the high street. Control two came at Great Waldingfield, where I greedily spooned soup from what looked like a dog bowl.

We resumed at a moonless 3am, looking forward to the sun rising in an hour or so. A cockerel crowed at 4.15am outside Barking, and place names became surreal. Nedging-with-Naughton? Cretingham? The final checkpoint at Earl Soham village hall, 18 miles from the finish, was a scene of disintegration. Adults sat sleeping in foot-high nursery-school chairs, their legs streaked with oil. One man gazed at me like a child, seemingly on the verge of tears.

I reached the purple heather of Dunwich Heath at 8.15am, in good time for breakfast. Weary pedallists swapped tales of the road, including the one about the ambulance man who fell asleep in the saddle, rode into a ditch and had to call an ambulance. And the two chaps from a central London bike shop who missed a turn labelled "easily missed" and cycled an extra 50 miles. The man on the Raleigh Shopper had, sadly, abandoned, but a woman on a three-speed made it. Chains came off and tyres punctured, but repairs were kindly and skilfully executed on the dark verge by fellow travellers. In total, 320 people paid the entry fee, 291 started and 272 finished.

Patrick Field sums up the central tenet of the ride: "Once you have the idea that you can connect the countryside to the city, it's as if you do live in the countryside," he says. "People ask me 'What do you get for your pounds 19.50?' Well, you get tea, breakfast, a swim in the sea ... In the evening, you know you can cycle to the Suffolk coast. You may never do it again, but you know that you could. That's the idea."

Dozing happily on the bus home, I too understood. I had the knees of an old man, but, for the moment at least, the mind of a wise one.

For details of organised rides and cycling in general, call the Cycling Touring Club (01483 417217), London Cycling Campaign (0171-928 7220) and British Cycling Federation (0161-230 2301). The 1998 Dunwich Dynamo is on 11 July; details from Mosquito Bikes, 123 Essex Road, London N1 (0171- 226 8841/8765).