Portugal's Upper Douro Valley is a hot attic room in the rambling mansion of Iberia. I first visited 18 years ago. Tractors had, by then, replaced the squeaking bullock carts remembered by old Douro hands, but in other respects it remained a journey to wallow in for those prone to agricultural nostalgia.

The scenes around the granite treading tanks, in particular, were Brueghelesque: dark eyes and ruddy cheeks gleaming by lamplight; the smell of sweat mingling with the heady sweetness of trodden grapes; old legs and young legs, all stained purple, mingling in a sticky, stately dance through the pip-choked must; and a kind of Dionysiac madness lurking just outside the door, held in check by the clipped, public-school-accented Portuguese of the British owners. The wild hills beyond, though, were as thickly scattered with farms as the night sky was with stars, and there were no clipped tones to be found in most of them. If Euripides' Dionysus, "most terrible, yet most gentle, to mankind", had gone to ground in any corner of old Europe, one felt, it must surely have been here, in port wine country.

Then day would dawn, and you would rub your eyes at disbelief when you saw the landscape which confronted you. This was viticulture as a branch of mountaineering. The river Douro (Portugal's continuation of Spain's Duero) cuts its way through a sea of schist between the Portuguese border and the granitic Minho, but it is a sea whipped to a force nine fury by past geological happenstance. In the central part of this region, around the town of Pinhão, a farm's highest vineyards may tower 500 metres over its lowest. Centuries of sweat have seen these soaring rockfields terraced into a kind of vineyard domestication, but one of daunting laboriousness. Side valley succeeds side valley, tugging about the main flow of vineyards; the terraces weave their way along the shuttling hillsides like relief lines on a map. Many travellers are reminded of Inca fastnesses, especially when the night mists linger in fingers and lozenges on the morning river below; after a glass or two, you might imagine yourself in a green Egypt, where mad Pharaohs had ordained the vine-planting of giant pyramids. It is a landscape to fire every cylinder of the imagination - yet tourism had left it, until very recently, the preserve of the hardy independent.

And, I should add, the train spotter. Europe's largesse has now kick-started Portugal's road-building programme, but until very recently the only easy method of travelling from Porto to Pinhão and beyond was via the magnificently stately Spanish-built railway. It's slow, it's cheap (E12.20 for a first-class one-way ticket), all of human life climbs on and off along the way, and the views (through the open doors and windows) are compelling. Creating the track must have made someone a dynamite fortune. Two further narrow-gauge railways, moreover, still serve the major side valleys, one running from Peso da Régua to Vila Real, and one from Tua to Mirandela. Hurry, though, if you want to use these; the fiscal axe, rumour has it, is being sharpened. Portuguese railways resuscitated a steam train to complete the return journey from Porto to Tua once a week, on a Saturday, but the puffer caused so many trackside fires that the service had to be suspended.

Transport was one reason why the Douro never received the visitors its beauty merits (I rate it, along with the vineyards of the Mosel and the Cape, one of the three most beautiful wine regions in the world); the other was accommodation. Here, too, the last decade has seen immense change. There are now a number of wine farms with rooms available for hire, such as Quinta de la Rosa or Quinta do Passadouro; old farm buildings high on the hills, too, have been restored for self-catering accommodation, like La Rosa's Lamelas and Amarela. Port company Taylor led the way with hotel accommodation when it converted one of its old riverside warehouses in Pinhão into a four-star, air-conditioned 40-bed hotel called The Vintage House; it has now sold this on to local entrepreneur Mario Ferreira, who owns some of the cruise boats which ferry 400,000 boat trippers up and down the river each year. There are more graceful tourismo de habitação (manor house tourism) options available, too, like the pretty Casa do Visconde de Chanceleiros, which combine basic hotel comforts with a sense of Portuguese ease and charm. Tourism in the Douro is about to take another leap forward, too, with the planned opening next year of a French-owned, luxury 'destination hotel' at Quinta de Romaneira, complete with helipad and lovingly renovated vineyards.

Once in the Douro, if you did nothing but sit on a chair, adjust your straw hat and marvel at the landscape you wouldn't have wasted your time. It's easy to watch the life of the vineyards unfold around you, since there are no secrets at all here, and everyone has a dress circle view of everything going on within a ten-mile radius. Few of the port companies as yet have official tours in the Upper Douro, since they concentrate their activities in the warehouse district of Vila Nova de Gaia, opposite Porto. But if you stay at La Rosa or Passadouro, you can find out all about the farm activities; book at vintage, and you can even climb into the tanks and tread away for yourself. Fishing, swimming and viewing the prehistoric cave paintings at Foz Côa (precious enough to have stopped a planned dam from having been built) are other options, and the local towns and villages are always spectacularly sited and rarely spoiled. I would find it hard not to jump on and off the lumbering, friendly train which rolls up and down the river; the region is an eye-brightening challenge for photographers and painters, too.

And, of course, you will never be short of a drink. Most wines taste at their best when the evidence of their creation fills the air around you; but there's something almost sacramental about a glass of tempestuous, inky-sweet port drunk when the mountains from which it has been wrestled glower at you through the late afternoon haze, or pump another ferocious day's heat back into the dark, uncaring universe.