Nelson's greatest triumph took place off the Costa de la Luz. Cathy Packe follows him beyond Cape Trafalgar

A lighthouse marks out the headland that gave its name to one of the greatest battles in Britain's naval history. Cape Trafalgar is one of the most remote spots on Spain's southern coast, a magnificent windswept promontory. You can see for miles, along sandy beaches that are almost deserted, even in summer. But 199 years ago, within sight of this bleak headland, Lord Horatio Nelson won the Battle of Trafalgar and lost his life.

Tenuously attached to the south-west coast of Spain, Cape Trafalgar is the wild and windy apex of a triangle to melt the heart of the most battle-weary tourist. Some 30 miles to the north is Cadiz, a major seaport and the largest town on the coast. In the letters he wrote during his naval career, Nelson did not refer to the remote beauty of this coastline, but in a letter written from his ship, the Theseus, in 1797, he records watching the ladies "walking the walls", a reference to the daily promenade that is still a popular pastime along the attractive Cadiz seafront.

There is much in modern Cadiz that Nelson would still recognise. The old town is a well-fortified enclave protected by solid walls; even the residential streets are built so close together that they might be trying to keep out unwanted visitors. The bastions of La Candelaria and El Bonete, which guard the city's northern and eastern corners, date from the 17th century. The castle of Santa Catalina was built after the Spanish were defeated by Anglo-Dutch forces in 1596; although Cadiz was already fortified by this point, King Philip II realised that reinforcement was needed. Work on the castle of San Sebastian, just around La Caleta beach, began in 1706; by the time Nelson was moored offshore, its tower served as a lighthouse.

Cadiz has expanded beyond its old walls, but visitors rarely linger in the modern city - a long finger of land jutting out into the Atlantic Ocean. Its ordered ranks of high-rise buildings are packed tightly, jostling for space in an overcrowded strip. This glimpse of modernity is rare, though, on the Costa de la Luz - southern Spain's Atlantic coastline. White-washed villages like Conil, once the centre of the tuna-fishing industry, refuse to change. Despite its increasing popularity with summer visitors, Conil remains a traditional Andalucian village.

It is this unspoilt quality, rare for a Spanish costa, which gives Spain's southern seaboard its charm. There are signs of development, of course; Tarifa, at the south-eastern end of the coast, is a popular windsurfing resort; and 200 miles away, the development that characterises Portugal's Algarve has begun to infiltrate across the border at Ayamonte. But the high-rise buildings and crowded motorways that have blighted parts of Spain's Mediterranean coast are nowhere to be seen here. Many residents are confident that the planners have learnt from their mistakes. Modern developments are springing up like mushrooms around the sprawling golf courses of Islantilla and El Portil that draw visitors to southern Spain. But the buildings are designed in traditional styles, to blend in with the old fishing villages and unspoilt pine forests that remain along the Costa de la Luz.

The lack of commercialisation of this part of the coast is due in large measure to the existence of the Coto de Donana, the largest national park in Spain, more than 500 square miles of marshland which is the natural habitat of hundreds of species of birds, animals and flowers. Located midway along the coast, Donana cuts the region in half; through traffic is forced to take a long detour around Seville. Visitors are encouraged to visit the park, exploring the walking trails that are marked out from the five visitor centres. Guided excursions by four-wheel drive depart from El Acebuche, and there are boats that cruise along the Guadalquivir river from Sanlucar de Barrameda, stopping a couple of times inside the park.

Sanlucar first attracted the attention of the British in the 18th century because of the fortified manzanilla wine produced here. This dry sherry acquires a distinctive, salty taste from the sea air of the Guadalquivir estuary.

There is no shortage of maritime heroes who have been associated with the Costa de la Luz, but there is one in particular of whom the locals are particularly proud. Not Drake, of course, who delayed the departure of the Spanish Armada; nor Lord Nelson, who inflicted an ignominious defeat on the Spanish in October 1805; but Christopher Columbus, who set out from a small coastal village near Huelva to sail across the Atlantic and discover America. A monument to the explorer stands at the mouth of the Rio Tinto; Columbus prayed at the Convent of Santa Clara in Moguer on the night before his departure. Nearby is the monastery of La Rabida, where he persuaded the Spanish monarchs, Ferdinand and Isabella, to fund his voyage of exploration. And below, at a newly constructed harbour, are replicas of the caravels in which he and his crew sailed to the New World.

Columbus left behind a region which, even five centuries later, is largely undiscovered. Ships still sail out of Cadiz, most of them tankers shuttling across to Africa. And there are plenty of pleasure craft on the water, yachts whose sails catch the wind that whips along the wide Atlantic beaches. For them, and the visitors who have so far found their way to the Costa de la Luz, the attraction is a combination that is increasingly rare: an unspoilt coastline that has not yet been discovered by the masses.

British Airways (0870 850 9 850, flies from Gatwick to Seville and Faro, across the border in Portugal. Services are operated by GB Airways. A special fare of £69 return is available for customers who book by 7 May, subject to availability