'You can walk all day in the Cheviots and never see another soul.' That's what they all said and, for the first half hour, climbing out of the upper Coquet valley on to the lumpy heather moorlands with only sheep for company, that was how it seemed. Then we realised that the dark cluster ahead of us was not a stray stand of conifers but a bunch of soldiers in camouflage gear. They turned out to be part of the Dutch army training on the Otterburn ranges at the southern end of the Northumberland National Park. They stayed with us for a couple of miles, chatting excitedly at the sight of all these hills and dales. A few hundred yards behind came half a dozen grim-looking instructors from the Parachute Regiment, their guns and radios a reminder that this was border country, always closely linked to warfare.

The Romans built camps here before retreating behind Hadrian's Wall, and William the Conqueror marched back down the Coquet after giving the Scots a slap as a prelude to three centuries of raiding and skirmishing. We shook off our military escort at the border ridge where we turned north along the the last section of the Pennine Way, looking across at the Scottish lowlands under weak sun streaming here and there through banks of cloud. We passed the pile of rocks on the 2,000ft summit of Windy Gyle, named for a day like today with the breeze sharp enough to take your ears off. Now we were well clear of Otterburn, with its red flags and trudging squaddies, and it was indeed deserted and peaceful with fans of afternoon sunlight falling into the steep valleys. The hillsides were covered with the pale grass which brought the name of 'the white country' to the Cheviots, and each hidden valley had its dry-stone sheepfold, perfectly circular and beautifully constructed.

Even the Norwegian spruce acquired an alluring turquoise tinge in the low light, and the only puzzle was a small flock of sheep in the village of Barrowburn with orange fleeces - not just the odd blob for identification, but a whole overcoat. The Cheviots are only one of three parts of Northumberland that offer fine walking routes, mostly neglected as people rush past to get to Scotland or go instead for the overcrowded dramas of the Lake District. The other two are the coast, and the central strip of hill and moorland country divided from the Cheviots by the River Till as it flows northwards to join the Tweed. 'The north-east suffers from the misconception that it's covered in slagheaps and coalmines,' says Ron Shaw, a retired tourism official who's helped develop walking in the region. 'That's only true of the bottom corner. The rest is the most unspoilt part of England. There are far more sheep than people.

'Whichever way you go, there's not only delightful countryside but a wealth of interest since prehistoric times. And it's ideal walking country, especially on the coast.' In the Cheviots, it's mostly an in-between kind of walking, ideal for the time when you want more than a lowland amble but don't fancy getting your hands dirty on cold, hard rock. The mood is more spacious and reflective, the stride more relaxed and rhythmic, than in really mountainous areas such as Snowdonia, the Lake District and the Western Highlands of Scotland. The central crags and dales have wide views and a varied terrain while the warlike past has left more castles, fortalices, peles, bastles and barmikins than you can shake a stick at.

But perhaps the greatest rewards are on the coast, where you can walk for miles along beaches and dunes with the sea air filling your lungs as the breakers roll lazily up the shelving, red-golden sand. The coast is a natural candidate for a waymarked, long-distance path, with all the brouhaha that would bring with it. But so far, fortunately, it hasn't happened and, apart from the last gasps of the Pennine Way, the main long-distance route in the county is the St Cuthbert's Way.

This leads from Melrose, where the seventh- century saint began his ministry, to Holy Island, where he was buried and his followers later produced the Lindisfarne Gospels. Devised by Ron Shaw, it's a 62-mile route, covered comfortably in a week. There is a pub on Holy Island and, if you're cut off by the tide there, it just seems to stay open. Ten miles south, you come to the huge hilltop fortress of Bamburgh. The village has a cricket field below the battlements, several small baronial-style hotels, and a Grace Darling museum. She was the one who rescued nine shipwrecked sailors in an open boat in 1838, only to die of consumption at the age of 26.

But perhaps the most spectacular castle is the ruin of Dunstanburgh, nine miles south of Bamburgh and three to the north of the little fishing village of Craster. It's hard to look at the gaunt silhouette without medieval cliches flooding into your head: the ring of sword striking helmet, trumpets sounding from the battlements, Mel Gibson rolling his eyes... My companion on the walk to Dunstanburgh was Carole Field, the local Liberal-Democrat councillor who runs a bed and breakfast in Beadnell, said to be the only east-coast port where the harbour actually faces west. We headed across the wide, damp sands of Embleton Bay, where the sand dunes behind the beach support an eccentric cluster of wooden shacks and bungalows staring out towards Norway.

As we came closer to the fortified headland, the beach turned into a great, rough pavement of black boulders, just right for one of those catapults they used to break down castle walls. Carole was outlining a siege plan of 'more visitors for Northumberland, but no more development' - she's just beaten off a a caravan site application from the mighty estates of the Duke of Northumberland.

'And it's just not true that the weather's bad up here,' she said. 'We're on the dry side of the country and we have warmer summers now.' As if on cue, a chink appeared in the grey canopy above us, and for a few minutes a shaft of sun lit the castle's mighty gatehouse.

Best guides

1 Ordnance Survey Landranger maps (1 inch in to 1 mile) nos 74 (Kelso and Coldstream), 75 (Berwick) 80 (Cheviot Hills and Kielder Forest) and 81 (Alnwick & Morpeth). OS Outdoor Leisure map (2 inches in to 1 mile) no 16 (The Cheviot Hills).
2 Walking in Northumberland, by Alan Hall, Cicerone Press, £7.99. ISBN 1852842652.
3 100 Walks in Northumbria, Crowood Press, £8.99.
4 Walks in High Hills Country, 18 walks in the Cheviots. Northumberland National Park Authority, South Park, Hexham, Northumberland NE46 1BS (01434 605555), £7.95.
5 Exploring the Northumberland Coast. Northumberland Countryside Service, County Hall, Morpeth, NE61 2EF, £2.50.
6 St Cuthbert's Way Summary Guidebook. Borough of Berwick-upon-Tweed, £1.50.

The practicals

Transport: GNER main-line trains to Newcastle and Berwick-upon-Tweed, with some services stopping at Alnmouth. A local train from Newcastle to Berwick stops at all stations. Accommodation: listings in the official holiday guides from Northumbria Tourist Board, Aykley Heads, Durham DH1 5UX (0191 375 3000); Alnwick District Council, Allerburn House, Alnwick, NE66 1YY (01665 510505); and the Borough of Berwick-upon-Tweed, Wallace Green, Berwick TD15 1ED, (01289 330044).