Northumberland; For those who love nature, walking, and English history

In some parts of the world, boundaries are little more than a line drawn on a map. This is the way you'd expect them to be in the peaceable old British Isles: mere administrative divisions with no more meaning than slight differences in local government and perhaps rather exaggerated or amusing traditions of local identity.

But anyone who chooses to take a vacation and deliberately confine it to one county (not a bad premise for a visit to a country that specializes in intimate details) may well discover that the word boundary not only adds zest, but also carries a historical significance closer to frontier.

Take Northumberland, for instance - England's most northern county, one of its least traveled, one of its least industrialized (confining its coalfields to a limited area in the south east corner), and as sparsely populated as any part of England (a mere 288,000 inhabitants). It's a marvelous county for certain kinds of travelers. It appeals to nature-lovers, to walkers, and particularly to people with a bent for English history. It has more castles in it than any other county in England, many of them now attractive and preserved ruins. It played host to countless battles. The remains of ''pele towers,'' or houses that were also strongholds, are still a notable feature. There are some fine country houses open to the public.

Once considered a wasteland, Northumberland is today pastoral and largely given to agriculture. It has more than a million sheep. Large tracts of it are national park and nature reserve. In its Cheviot Hills, which form its west side , it has expansive, stimulating scenery.

Sometimes desolate and wild, these hills have a free and open relationship with the wide sky, which is unlike anywhere else I've seen. The county also has , in the east, an amazingly unspoiled coastline and fine, if rather chilly, beaches. Parts of this are a bird watcher's paradise, with, offshore, the 28 rocky Farne islands, which were once a sanctuary for early Christian saints and now are a sanctuary for cormorants and kittiwakes, shags, oyster catchers, guillemots, puffins, and herring gulls. The isles can be visited by boat (though the only time I tried, some years ago, we were turned back by the weather). The Farnes are also the only breeding ground along the northeast coast of Britain for the gray seal.

But what distinguishes Northumberland more than anything else is that for centuries it was indeed a ''frontier'' land. In a way, it still is, particularly if you approach it, as my wife and I did recently, from the north.

You can enter the county high up on a ''neck'' of land in the Cheviots called ''Carter bar.'' It is exposed and lonely, full of empty space. From this point on, everything in your journey seems downhill. You are crossing the border from Scotland into England, and it is not at all difficult to visualize this steep fell countryside as rife, long ago, with raiders and sheep stealers and marauders -- wild, hairy plunderers (who crossed in both directions, whatever the English may have been brought up to feel about the Scots as the invaders, or vice versa). You really do feel, as you ride over this border -- which is made even more of a no man's land by an unexplained gap between the boundary signs - that you are moving dramatically from one ancient kingdom into another.

Northumbria was indeed a 'kingdom' centuries ago, but far larger than it now is. It stretched from the River Humber in the southeast to the Firth of Forth in the northeast, up as far as Edinburgh, that is.

The Scottish capital originally got its name from one of the Northumbrian kings, Edwin. It wasn't until 1844 that the county boundary (as it was until 1974) was ''finalized.'' Its northernmost town was, and still is, Berwick-upon-Tweed, and its southernmost, Newcastle-upon-Tyne. But even that changed eight years ago when Newcastle, which was always by far its largest and most populated city, was separated.

If, on your holiday exclusively devoted to Northumberland, you stray as far as Newcastle, you are out of bounds. Nor can you jump over the borders to the south and west in either County Durham or Cumbria. But there is one very old boundary you are allowed to cross, one which is both literally and figuratively a high point in any Northumberland vacation. You can, in places, even take a walk along the remains of it. In a way, it is like the backbone of some vast sleeping serpentlike creature, stretching across the county from east to west and beyond, emerging out of the earth of the centuries at intervals.

At each reemergence it is nowadays surrounded by care and attention, information and turnstiles. It is preserved and presented as the extraordinary ancient monument it is. Described in the title of a book about it as the ''north west frontier of Rome,'' it was built because the Roman Empire (to its shame) was unable to subdue the Scots. It is Hadrian's Wall, known by Northumbrians simply as ''the wall.''

Today, this ''moving impression of imperial power and purpose,'' as Robert Newton calls it in his fine book on the making of the Northumberland landscape, is visited even in winter by hikers and sightseers in search of the bracing blend of history and very fresh air it offers. It is carried by Northumberland's most notable geological feature, the ''whin sill.'' This was formed 200 million years ago by deep subterranean upheavals forcing molten lava to the surface. It links various parts of the county together. By the coast, it is the same whin sill that provides the great rocks on which the castles of Bamburgh and Dunstanburgh were built: One is restored, one is a ruin; both are visitable. Out at sea, the whin sill again crops up, this time as the aforementioned Farne Islands, with their ''pinnacles,'' or columns of basalt, a perfect habitat for sea birds.

My wife and I came home from our recent short trip into Northumberland with a fairly jumbled assortment of impressions. She recalls first and foremost the long straight roads (there is one running parallel to Hadrian's Wall) which streak relentlessly across this ''land of far horizons,'' to use G.M. Trevelyan's phrase.

I particularly liked the grounds of the house which belonged to the Trevelyan family, Wallington, now in the hands of the National Trust. We were treated to an extensive tour of this unpretentious 18th-century country house. Its grounds are extensive and beautiful, and in part ''may'' have been laid out by Capability Brown, the great landscape gardener, who, much more definitely, did go to school in the tiny and endearing village of Cambo nearby. There is an unusual walled garden at Wallington, with a stream running through it. This garden is tilted and sloped (not unlike an echo of the whole county as it slopes from the Cheviots down to the sea). It seems to slip away under your feet. The greenhouse contains two staggeringly tall flowering fuchsias, about 70 years old.

Neither of us will forget the night we spent in what must surely be Northumberland's most entrancing and unspoiled village, Blanchland. You can't go farther south in the county than this. You reach it over open moorland which, by contrast, makes it seem all the more nestled and cozy. Blanchland church is part of the remains of a 12th-century abbey. The gatehouse hails back to the 15th century. And the village inn, the Lord Crewe Arms, originally the abbey guesthouse, is inextricably tied up with a mixture of Northumberland family histories, romance, heroism, and folklore.

The night we spent here will go down in our own family history as the night of the four-poster bed. The clean little room, merrily decorated in Laura Ashley wallpaper and fabrics (as was the bed itself), was virtually filled to capacity with this four-poster. We were so taken with it, there was even talk at one point of converting ours at home. Perhaps it was the spider that showed up on its ceiling in the morning that tipped the balance against the idea -- otherwise we were very comfortable, private, and self-contained. Each room in the hotel is named after some notable hero or heroine of the abortive Jacobite rebellion of 1815. Ours was Radcliffe. On inquiry, I discovered that this is the only room with a four-poster, so if you want it, make sure you ask specially for it.

Over breakfast (the food turned out not to be the Lord Crewe's strongest asset) we gazed out of the window at pastureland enhanced by fine old trees, placed in the view with the immaculate taste of . . . when? The 18th century? The 17th? Or earlier still?

Drive up the hill in one direction out of Blanchland and you are with startling immediacy in County Durham. This won't do, of course, so you turn round and head north, back into Northumberland -- in search of what? You might fancy the most comprehensive selection of vintage tractors and engines in the United Kingdom, the Hunday Museum at Newton, three miles from Corbridge. Or Corbridge itself, with its intact vicar's pele, or fortified vicarage. Or nearby Costopitum, the remains of a Roman town.

We went to Hexham, a busy market town with an ancient abbey. Its crypt is Saxon and famous, composed, as Sir Nikolaus Pevsner has said, ''of narrow vaulted gangways and chambers comparable to Roman catacombs.'' In fact, the stone had previously been in Roman hands. The Saxon builders took it from the remains of ''the wall'' -- by that time long abandoned by the imperial power, after 300 years of rule.

We enjoyed climbing the monk's ''night stair'' in Hexham Abbey, relishing the strange pleasure of stone steps hollowed and humanized by years of habitual tread.

I was keen to visit a place called the World Bird Research Station at Glanton , run by a father and son, Calvert and David Noble-Rollin. Anyone who visits this ambitious-sounding establishment is in for a surprise, first, at its smallness, second at the enormous collection of birds that live and are bred and studied here, and third, at the worldwide activities of its two directors.

Mr. Noble-Rollin Sr. had just come back from one of their frequent bird-studying trips abroad. His enthusiasm and originality are engaging. We left with all kinds of fresh insight into bird behavior, a confused memory of his description of what the dawn chorus must have been like in prehistoric times; a vision of duck that had been bred backward so that the latest generation looked like its earliest progenitors; and a persuasive pamphlet that reverses the dogmatic theory of heredity as the sole cause of albinism in blackbirds. Biologists are apparently so dyed in the wool of heredity, of white blackbirds turning white because of inherited traits, that they can't accept Mr. Noble-Rollin's proofs; but he doesn't seem to mind too much. Northumbrians are known for their independent attitudes.

On we drove to Rothbury, which lives most attractively up to its reputation for captivating scenery. By the River Coquet, it is a good touring center, and is loved by keen walkers. A medieval bridge, and a gorge called the Thrum, are striking features of Rothbury, and Brinkburn priory, founded about 1135, is a monastery to visit.

In a fine woodland and riverside setting, afternoon tea at a little light-bite cafe called the Sun Kitchen is strongly to be recommended. But the thing that bowled us both over in this town was Cragside Hall.

As it was winter, this Victorian mansion was closed to the public. But the grounds were open, and its spectacular exterior could be seen. What a place it is. When the rhododendrons and azaleas are in flower, it must be astonishing to drive the six-mile road around the estate. A wealthy industrialist, inventor, and gunmaker bought Cragside in 1863 -- the first Lord Armstrong. He added to his land until it was approaching 2,000 acres.

He planted and landscaped it with an extraordinary mixture of the scientific and the imaginative. The house itself, concocted by Richard Norman Shaw as an astonishing hodgepodge of 19th-century neo-Tudor and alpine fantastical, was actually an enlargement of a small existing house almost lost among the huge crags surrounding it.

It is no longer lost. It is a breathtaking house from the outside, the visual climax of a hillside of boulders and tall pines and a stream spanned by picturesque bridges. It is both preposterous in its ambitions and oddly thrilling in its boldness. On our next visit, we fully intend to see the interior of this wild and wonderful Victorian house.

Lord Armstrong was the first person in the world to have his house lighted by water-powered electricity -- in 1878. His lifts were hydraulically operated. He also built a whole series of lakes in his grounds. His fascination for water and its power would have made him more than interested in a very recent addition to the Northumbrian scene -- which is also going to have to await our next, perhaps longer, visit. This is the Kielder Dam and reservoir, constructed in the western hills.

It is one of the largest man-made lakes in Europe, with a storage capacity of 44 thousand million gallons. It is situated in a part of Northumberland that can hardly be described as treeless - the quarter-million acre Kielder forest, also man-made.

All we had time for on this occasion was a quick run up the coastline, with a hasty detour to Lindisfarne, the ''holy island,'' which can be reached, when the tides permit, by causeway. The weather had been perfect for our trip, and the sun set now, spreading its gold over the ocean, setting off the romantic shape of Lindisfarne Castle, high on its rock, neatly restored this century by Lutyens. This made a decisive image -- a kind of grand, final chord -- with which to end our Northumberland visit.

Darkness fell as we headed north again, via Berwick-upon-Tweed, to Edinburgh and Glasgow. We felt as if we had been thousands of miles from home. In many ways Northumberland seems to belong to primeval lands and remote peoples. Even that last glimpse of the small island of Lindisfarne was a glimpse of one more extraordinary historical event. It was here, if anywhere, that Christianity was first introduced to England, by a missionary invited to his kingdom by King Oswald. The site of St. Aidan's monastery is there, though replaced by an 11 th-century monastery which still stands. Surely, Lindisfarne is one of earth's remotest borders: not a bad place to start such a momentous ball rolling.