Many frontiers are vague, meandering affairs, shaped by politics rather than geography. But there's a section of the border bet-ween England and Wales that is one of the world's most natural, and unambiguous dividing lines. It's a clear, straight ridge of more than 10 miles, and it offers one of the best walks in Britain.
This is Hatterrall Ridge, the easternmost outlier of the Black Mountains - the range between Abergavenny in the south, and Hay-on-Wye in the north. It boasts stirring views and the freshest air, and tucked behind it is the beautiful Vale of Ewyas and the ruins of Llanthony Priory.
Whether you're an experienced walker or pulling on a pair of boots for the first time, this is a fantastic place to come if you want a good, long trek. Your starting point is the priory's car park, reached in three hours by car from London via the M4 and the A40 through south Wales, or by train to Abergavenny, and a 12-mile taxi ride. Built into the ruins of this 12th-century Augustinian abbey is a small hotel and bar, into which you will probably collapse on your return.
Armed with the Ordnance Survey Outdoor Leisure Map No 13 (Brecon Beacons National Park, eastern area), walk back to the valley road, down the lane opposite and over a footbridge. Follow signs for the Cwm-Bwchel path, which leads into the cleft in the hills in front of you.
It's a stiff climb, but soon you're 700ft higher, striding across heather moorland, with Hatterrall Ridge behind you on the other side of the Vale of Ewyas. The rest of the Black Mountains are in front; their northernmost summit bearing the elegant name of Lord Hereford's Knob.
At a meeting of paths, at the spot marked Bal Bach on the map, turn left and south towards a rounded, eight-foot-high cairn. From there continue southwards on a clearly marked path for about four miles, looking left across the valley to Hatterrall Hill and the cliffs of Cwmyoy Darren.
This brings you to the foot of the ancient hill-fort of Twyn-y-Gaer, which offers a quick 200ft detour, before you resume the track for another mile, straight down to the Queen's Head inn at Pont Rhys Powell. The inn has decent food and beer, and a chatty landlady.
From here, there is a mile of uphill country lanes as you cross the river and take a right, then a left, to arrive at the dramatic viewpoint near Upper Pentwyn, where you can stare for miles across Herefordshire, just as the Celts might have done 1,500 years before. Nowadays it's a jumping-off point for hang-gliders.
You're now on Hatterrall Ridge, heading northward on Offa's Dyke path, a national trail. For much of its route, the path follows an impressive earthwork, constructed in the eighth century by King Offa of Mercia to mark his boundary against the Celts. This is the highest section of the 177-mile trail, which runs from Chepstow in the south to Prestatyn in the north.
Keep going along the spine of the ridge, passing an old trig point at 1,521ft. If the day is clear, you'll enjoy magical views of the Vale of Ewyas and Llanthony Priory on your left. Two miles after the trig point, take a path which turns down towards the priory. Don't cross from the moorland into the fields until you reach some ruins by a stream; then cross a stile, a field and a wood, and the longed-for pint will be yours.
That's a good 13 miles. For a shorter, eight-mile version of the walk, cut out the first ascent and the Bal Bach section. From the priory car park, go back to the valley road, turn left and walk southwards until the first bend. Cross the stile and follow the track straight ahead, which will take you through the farmyard of Maes-y-Beran.
Ford a stream with a waterfall on your left, and continue for a mile and a half through copses, with the crags of Cwmyoy Darren beetling over you. Pass St Martin's church in the village of Cymyoy, and follow the sign to Hatterrall Hill. You then stick to a path against the south-western flank of the hill for about a mile, before climbing steeply through heather and bog to reach Offa's Dyke path on the ridge, and join the route described above.
A third variation would be to climb straight up to the ridge from Llanthony, turn north along it, and walk more than four miles, then return to the valley at the Vision Farm, near the village of Capel-y-ffin.
For other walking routes around the country, simply choose an area. The Ramblers Association has good ideas for walks, and it's worth joining the organisation if you're interested in group walking or campaigns.
For several days or even weeks of continuous walking, the 13 national trails pass through some of the best countryside in England and Wales. They're maintained by the Countryside Agency, whose website is a good starting point for information. In Scotland there's the West Highland Way from Glasgow to Fort William, and a vast range of mountain walking, including the 284 Munros - peaks over 3,000ft - and the fearsome Cuillins, on the Isle of Skye.
The British Mountaineering Council caters for walkers as well as climbers, with 15 detailed routes in each monthly edition of its magazine, Trail.
Ireland has a big network of long distance paths (try ireland.travel.ie). Further afield, France has the huge GR (Grande Randonnée) network, including the GR5, through the southern Alps from Lake Geneva to Nice.
Several holiday companies such as Inntravel, ATG Oxford, and Ramblers Holidays (see the Ramblers Association website) organise comfortable walking holidays in western Europe, mostly with your luggage transported for you from hotel to hotel.
But if you're feeling more macho, just take a backpack and a tent and follow the ridge of the Pyrenees (which will take you 50 days), the GR20 in Corsica (14 days), or the Haute Route from Chamonix to Zermatt (14 days). You'll end up with a real sense of achievement and very firm thighs.
These boots were made for...
Waterproof, lightweight or with extra support for those 20-mile treks? Get a grip on walking boots with our selection of the best on the market.
Scarpa Manta M4, £144.99
The best for the toughest winter conditions, plus they can be used with crampons for extra grip on icy ground.
Meindl Burma, £124.99
Strong, waterproof and good for general, three-season use on British hills and mountains.
Brasher Fellmaster GTX, £100
Supple, waterproof, good for summer use. Brasher boots are very light and big on comfort.
Salomon Exit Low, £60
A light, strong, multi-terrain shoe, good for moving fast in dry places.
Merrell Kona Convertible, £40
Essentially a waterside sandal, but they offer enough protection and grip for most summer walking. SC
Other essentials
After choosing the right boots, the most important piece of equipment for a walker is a waterproof jacket, preferably with a hood, and made from a breathable fabric like Gore-Tex or Sympatex.
Pack it in a 25-litre daysack with adjustable straps, along with a pair of waterproof over-trousers. An Ordnance Survey 1:25,000 map (two-and-a-half inches to one mile) and a compass should stop you getting lost.
If you're in the hills or off the beaten track, pack a survival bag, containing a small torch and a whistle, plus extra clothing, some high-calorie food and a thermos of warm drink. And always remember to tell a friend where you're going and when you expect to be back, so there's someone ready to raise the alarm if you should get stranded.
