Taking a country walk in Portugal can be frustrating, even with a large-scale military map, as some paths are public, others very private, and few are signed. However, Nick Symington - a member of the family that produces Graham's Port - has devised for the walking specialist Inntravel a circular trail full of interest, with accommodation in stylishly-renovated manor houses hidden deep in the countryside.

A group of us set off from Casal do Loivos, above Pinhão, along an ancient cobbled track that follows the crest of a ridge. We pass small family-owned vineyards and hamlets where even the simplest home displays the skills of the granite mason. There are far-reaching views across the countryside to Alijó, a small town blessed with a panoply of EU-funded projects including a theatre, a botanical garden and squares with clever water features. "What we really need is a modern hospital," a local woman says when I praise the works. "Ours is a disgrace." Once away from the Douro itself, it is clear that this remote corner of north-east Portugal is only now entering the 21st century. Abandoned mansions slowly crumble into gardens gone wild, bakers use ancient wood-burning ovens, and shops sell the kind of cheap Chinese goods that nobody else in Europe wants.

A particular highlight is the small town of Provesende, where the Lisbon nobility lived out their lives in miniature versions of their former palaces after being banished from the capital in the 1760s. Most of the mansions are in dire need of new roofs and windows, though several are shrouded in scaffolding. Today, even these former places of exile present an attractive investment opportunity.

The one-hour train ride from Pinhão to the end of the line at Pocinho must be one of the world's most scenic rides: the biggest names in port-making have their vineyards along this stretch, where the Douro enters a deep, narrow gorge. Every few miles there are little halts and, above the dam, the smooth flat-topped boulders are perfect places for picnics or for diving into the cool, clean water on a hot summer's day.

I am on my way to the Côa Valley, site of the world's oldest collection of outdoor art, discovered only in 1992. There are guided tours in three locations, led by professional archaeologists who speak good English. This was an important trade route up through the Iberian peninsula for at least 30,000 years and the shale cliffs are full of deeply incised carvings of animals, made using flints from Valladolid in Spain.

There are recognisable domestic cattle, horses, oryx, goats, even a salmon - and some of these animals have been drawn with several heads. "We think ancient travellers would have built a fire in front of such drawings to create light and shadow," our guide says. "As the breeze fanned the flames, it would have looked as if the horse's head was nodding, as in a flip cartoon book." Nearby, the village of Castelo Melhor has a Roman road, a medieval watermill and a picture-book 13th-century keep on a round grassy hill.

After a week, I feel I have only scratched the surface of this border country between Portugal and Spain. I did not have time to take a branch-line train to Mirandela or Vila Real; nor did I visit the château depicted on the Mateus Rosé wine label, or Lamego, where El Cid drove out the Moors. There is enough history in and around the Douro to keep visitors occupied for a month or more.