No geography O- level and no sense of direction: not a promising basis for planning a week's mountain walking in the Picos de Europa, in northern Spain. I decided to paper over the cracks in my orienteering abilities with a compass (easy-to-follow instructions included), three maps and a walking guide (hard-to-follow directions in Spanish).

I fretted unduly. Austin, my companion, has the homing instincts of a pigeon and knows a contour from a path. After a week in Spain he even tracked down the car in Stansted's long-stay car park.

The Picos de Europa are a magnet for Dutch, Belgian and Spanish walkers and climbers (and the odd Romanian mountain-biker) but are still relatively unknown to Britons. This is changing: the perimeter villages are sprouting hotels and gift shops peddling cider, venison chorizo sausages and clogs on studs.

The best protection the mountains have against this tourist tide is their damp climate and inaccessibility. To get much beyond the pretty valley villages you have to be prepared to huff, puff and rough it. We took backpacks, waterproofs and sleeping bags, but no tents, deciding to rely on hotels, hostels and mountain refuges. I just wish I'd packed a donkey for the uphill bits.

We'd done no route planning other than to pick a starting point: the village of Arenas de Cabrales, whose main street is dominated by a pink palace of a hotel. We checked in, admired the Swiss-valley view, and raided the mini-bar. It was not going to be an early start the next morning.

From Arenas there is only one road you can take into the central massif of the Picos. So we didn't need to think until 6km along, when we paused at a fork in the road for a tortilla sandwich and to toss a coin. By going right we inadvertently set our course for the whole week, landing up on the dramatic, glorious 12km traverse of the Cares gorge. Since no road follows this trail, to get back to Arenas we would have now to do the full circle of the central Picos massif - or else cut through the middle, across the mountains.

The Cares trail is solid and easy, leaving you free to gawp at the spectacular gorge that drops a kilometre down to a silver boiling froth of a river below. But what captivated me was an aqueduct that ran alongside us the whole way. There is an entire network of these little 2ft-wide canals, built in the Twenties as part of a hydro-electric scheme. For much of its journey the water flows inside the rock, reappearing at odd moments, now above, now below you. Where it emerges, it runs silent, flat and smooth, in perfect counterpoint to the turbulent roar below.

At the end of the gorge is Cain, a hamlet with a half-built hotel and a bus service on Thursdays. On Tuesdays, the only way out is to walk. The odd vehicle passed us, throwing up clouds of black exhaust. And then we passed one car, deserted, boot open, by the roadside. Two figures came into view round the bend, dragging a goat by the horns. Cheery and a bit stupid in the morning sun, I greeted them as we passed. They did not smile back. The boot slammed, the car revved, the men passed us in a black cloud, grinning. The penny dropped. 'Austin,' I said, 'That wasn't their goat.'

That was a good walk, though. On a crisp, early summer early morning the sun teased its way around, through and eventually over the rock slabs above us, casting the valley below in a palette of greens. To each side of us were the purest, gayest, most expansive wild-flower meadows I have ever seen. And at the end of a long climb was a mirador which gave us our first panorama of the central range of the Picos: steel grey with snow caps against a china-blue sky. It was breathtaking. And I was out of breath.

Our lunch and water- refuelling stop was to be the village of Santa Marina de Valdeon. Then we would leave the road for open country, where, with luck, we'd hit a mountain path all the way to our next resting place.

There was an ominously sleepy quality about Sta Marina. We found the sole bar- finca, but the busty bar owner, hanging out her husband's trousers from the balcony, was not encouraging. Could we get lunch here, I asked. No, she said. Isn't this the finca? Yes, she said, and this is Tuesday. The finca is closed on Tuesday. So, I hesitated: there's nowhere we can get food and water? No, she said. And slammed the shutters.

We filled our water bottles from a roadside standpipe, cursed Sta Marina and set off into contour country.

The rest of Tuesday was hard slog: the weather closed in, forcing us into rainproofs, and we split open an emergency raspberry flapjack. But the trail was clear and at its end was a treat: a new hotel with a fabulous restaurant.

Now halfway round our circular course, we took a shortcut on the region's only funicular, up into the mountains. Across snow, rich dark peat and an ocean of gentians we wandered, making such good time that by mid-afternoon we added an extension to the day's route, to draw us further into the central massif and the fabled village of Bulnes.

About 10 minutes after our switch of route, the weather began to fog up again. But this time our trail lay across an exposed hillside. As we reached its brow, dozens of trails stretched out in every direction, while a soupy fog obscured all useful bearings. We were lost.

Keep right, suggested Austin. No, left, I argued. Why do I say these things? And why did he listen? But I was encouraged by clacking cowbells and the crowing of a cockerel through the fog. Within minutes we came to a stone hut where a woman told us we were at the remote hamlet of Majada la Terenosa. Told you, said Austin: completely wrong direction. We should head straight down the hillside, he suggested, now that we knew where we were. Having got us into the mess I didn't argue, insisting only that we take a compass bearing.

Austin hung the compass round his neck and then followed his nose. We tramped down and down, through heavy, sodden grass, stubby burnt gorse and fields of yellow globe flowers, past shadowy huts, across a feeble stream. After an hour and a half the fog started to thin. By 8pm we had full vision and broad daylight again, and the village of Bulnes squatted just below us.

Bulnes is the sort of place travellers are proud to have been to. It is an hour's walk from the nearest road, so everything that goes in and comes out - beer, non-degradable rubbish and the dying - travels the same mule track. Electricity arrived only in 1989. Bulnes also happens to be absurdly picturesque.

The name of Bulnes is synonymous with the most distinctive and forbidding peak in the Picos range: the Naranjo de Bulnes. Proper climbers never call it this ('the Orange of Bulnes'), but everyone else does, because of the mountain's sheer orange- brown face.

All but skilled mountaineers settle for getting to the Urriello refuge which cowers at the base of this extraordinary mountain. There is a new tourist path: a safe, steady uphill three-hour trudge. But where's the fun in that? We were signing up for the traditional ascent, the masochist's route: from Bulnes village straight up a seemingly impassable waterfall, through a gully, round into a high meadow, up along an even longer gully and then across open fields to the Naranjo.

I fell over in the waterfall, but otherwise the first couple of hours were fun, part-walking, part-scrambling. We rested at the high meadow and it was sparkling and intimate and silent but for the wheeling crows.

The next hour was tougher, because the sun was higher. And then we hit snow. Above about 1,600 metres it was solidly packed, right through the long gully. I was completely unnerved, not knowing whether my heavy stamping to gain footholds would send me plunging through a bottomless hole, or start an avalanche. After two very slow hours of this, we emerged at a snowfield and I announced I was giving up: Austin would have to order a helicopter.

This man deals with awkward types for a living. He looked down pityingly, grunted, took my rucksack and headed off over the horizon. I sighed, and walked. Less than half an hour later the refuge popped into view, the other side of a snowfield criss-crossed by a half-dozen trails of bootprints. There wasn't much of a party going on up there at 2,000 metres: three Spanish chomping tinned sardines and two knackered but happy British couples. We bought iced-up weak Dutch beer and dried our sodden socks in the sun. Just being there was enough, subdued as we were from exertion and humbled in the presence of this mighty rock.

We went back by the tourist route. And as we numbed our bruised bones and blisters in the freezing stream at Bulnes we agreed our final two days' itinerary: hobble back to Arenas, check in to the pink palace, raid the mini- bar and sleep.

Getting there: the closest airport to Arenas de Cabrales is Oviedo. Aviaco (part of the Iberia Group; 071-830 0011) flies three times weekly from Stansted, and has a special offer of pounds 125 return until 14 October. From Oviedo, there are several bus services a day to Arenas de Cabrales, which take about two-and-a-half hours.

Recommended reading: Trekking in Spain by Marc Dubin (Lonely Planet, pounds 6.95); Spain: the Rough Guide by Mark Ellingham and John Fisher (6th edition, Penguin, pounds 9.99).

Further information: Spanish National Tourist Office, 57 St James's Street, London SW1A 1LD (071-499 0901).

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