Where Sherlock Holmes feared to tread

Simon Calder followed the century-old footsteps of Conan Doyle's detective into the uncompromising vastness of Dartmoor

DANGER AREA" screams out of the map of Dartmoor in red capitals. "Bleak House (ruin)" adds to the forboding. And the cartographic revelation that Devon possesses a Mountain Rescue Post might persuade you to stay in and read The Hound of the Baskervilles instead.

But Sir Arthur Conan Doyle may yet convince you to visit Dartmoor: "It is a great place, very sad and wild, dotted with the dwellings of prehistoric man, strange monoliths and huts and graves."

He wrote these words in a letter to his mother from the Duchy Hotel in Princetown while researching his celebrated mystery about a phantom hound and foul deeds. Dartmoor's central settlement has not changed much since 1901. The moor, the mist, the walls of H M Prison and the huddled houses all squeeze into a thin spectral slice of grey.

Dartmoor is England's last great wilderness, a slab of ancient rock rising from the soft fringes of Devon. Planes heading to America fly over it, but from 30,000 feet (fog permitting) it is just a big bald patch circled by neatly cultivated fields. From six feet, you shiver amid the stunted shrubs and perilous swamps, and look around at Conan Doyle's "crests of jagged granite foaming up into fantastic surges".

Fiction and reality collided one foggy night at the turn of the century while the celebrated crime writer was in the smoking room of the Duchy Hotel. The prison governor, chaplain and doctor came to visit, expressing a wish "to call on Mr Sherlock Holmes."

Holmes left town nearly a century ago. In his crime-fighting place are a few optimistic signs (perhaps aimed at the prison's 600 inmates) stating "This is a Neighbourhood Watch area." The hotel has closed down, too, and become a tourism office. Its ungainly neo-classical columns now draw tourists on the trail of Conan Doyle's devilish dog into the High Moorland Visitor Centre.

The way to comprehend Dartmoor is to feel it, to walk across its uncompromising vastness. Careful which direction you set out in, mind. Much of the moor is taken up by military training reserves, and "firing today" signs warn visitors against straying onto shooting ranges. Careful where you tread, too. You can almost sense a wizened old local, lips as cracked and blackened as the moor, whispering "Don't stray from the path".

There are three good reasons for taking such advice: the risk of trampling on live ammunition; the danger of disturbing ground-nesting birds; and the threat most chillingly revealed by Mr Stapleton of Merripit House. Pointing at Fox Tor Mire, he regales Holmes with the cheery news that "A false step yonder means death to man or beast. Only yesterday I saw one of the moor ponies wander into it. He never came out. I saw his head for quite a long time craning out of the bog-hole, but it sucked him down at last."

That sort of thing could quite spoil your holiday. Conan Doyle wisely commissioned a local, one Henry Baskerville, to drive him across the moor in a carriage. Mere pedestrians stepping out on their own should stick to a venerable trail such as the Abbot's Way. This ancient path linked the abbeys at Tavistock (now almost obliterated) and Buckfast (thriving, and doing nice ecclesiastical sidelines in honey and tonic wine).

You pick up the Abbot's Way southeast of Princetown, and follow it over a lunar landscape riven by infant brooks. When this was a great highway rather than a forgotten byway, the only fords were the stepping stones across the waterways. Deeper tracts are crossed on clapper bridges, slabs of granite slammed over gabbling streams. The track skirts Fox Tor, fords the embryonic River Plym and takes you into terrain so gothic that you are screaming to share your excitement and fear.

Tough. The only certainty at this time of year is that there is no-one with whom to talk. Dartmoor in the last week in February is as close to a physical manifestation of the word "wilderness" as you would wish. The nearest humans are probably the passengers in the 747 carving a jet trail six miles overhead. You are left with the ancients, whose standing stones and cairns deck the heath and heather to commemorate the long-dead. Occasional flashes of colour provide the only respite from this alien, monochromatic world. Patches of fern have been burnt and beaten into ruddy submission by sun and wind, matching the ochre tones of the iron-rich Red Lake Mire. Vivid green moss clings to the dark Dartmoor granite - the stone used for Nelson's Column, in Victorian mimicry of standing stones on the moor.

As you breast yet another subdued summit, the map suggests you are nearing the edge of Dartmoor. But if, like me, your luck begins to ebb away, the path will start to dissolve into the coarse, rocky grassland. You have two choices: to retreat into the gloom and try to find your way back across the moor, or to press on and hope your story does not end in some Baskervillean bog like that of Conan Doyle's villain.The book's denouement reveals that the life was not ripped out of Sir Charles Baskerville by a ghostly hound. The killer was the "cold and cruel-hearted" Stapleton who had earlier warned Holmes about the perils lurking on Dartmoor. He met his end hereabouts "in the heart of the great Grimpen Mire, down in the foul slime of the huge the morass which had sucked him in".

Take care out there. DANGER AREA is about right.

Dartmoor information: High Moorland Visitor Centre, The Old Duchy Hotel, Tavistock Road, Princetown, Devon PL20 6QF (01822 890414).

Safe walking: good boots, warm clothing and waterproofs are essential clothing. Follow Sherlock Holmes's example and "send down to Stanfords for the Ordnance map." Stanfords (0171-836 2411) and other map retailers sell the Ordnance Survey's 1:25,000 map of Dartmoor, price pounds 5.40.

Avoiding bullets: call 01837 52939 to find out what the army's training plans are, and watch for red flags and lights warning of live firing.

Good reading: the best edition of The Hound of the Baskervilles by Arthur Conan Doyle is the one published by the Oxford University Press, price pounds 3.99.