Travel: Stormy scenes of illicit love: Jonathan Sale takes the windy riverside path from Southwold, Suffolk, and enters a world of curiosities, fantasy and real romance

The couple stood on the footbridge over the River Blyth, looking pensively out to sea. They had their backs to the Suffolk countryside; they also had their backs to a man peering intently at them from behind a wall.

I could see him, and so could you - if you managed to catch The Bridge, the film based on Margaret Hemingway's novel. Ms Hemingway, who died last year, had been intrigued by Philip Wilson Steer's painting of the bridge between Southwold and Walberswick, and in particular by the tension lurking in the figures on it. Having discovered that Steer stayed in the area during the summer of 1887, she invented an adulterous love affair with the woman whom he painted.

This spot has a quite different significance for me. It is a handy starting point for a round trip that follows the north bank of the River Blyth to the next bridge and returns along the line of a narrow gauge railway.

Over the years, I have covered different sections of the route by foot, bike, boat, car - everything except by train, which was axed in 1929. But I have only once completed the walk's circle in one go, on a blustery day in late summer.

The strong wind was managing, despite having only the width of the river to play with, to whip up impressively large waves and crash them against the bank. The gale was tugging at the anorak of a bird- watcher 100 yards upstream from the bridge, and it was whistling dangerously round the decayed woodwork at the top of the old oast house beyond. It reminded me that, in 1953, a high wind and a high tide combined to swamp much of the East coast.

Forty years on, and even with a massive storm bank, no one takes any chances. When friends of mine moved to a nearby inn, the local police asked for the names of all members of the family, including the cats, in case a lifeboat were ever needed to rescue them. Not surprisingly, there was scarcely a house to be seen for the next mile, until I reached the bungalow where the road out of Southwold skirts the river's edge. There is generally a small boat moored here, which could turn out to be useful one day.

By now the south bank was a distant blur. The river balloons out to produce wide, shallow and muddy saltings on either side of a narrow, navigable channel. It is as if the river had its estuary inland from the harbour. The gale had a much greater stretch of water in which to let rip, and the short, fierce waves were casting spray over me.

It is another 17 or so lonely promontories until the next house. You cannot miss it: at the bottom of its garden is a pier large enough to take an ocean-going cruiser, although the water is about 18in deep. The director, Peter Greenaway, built this structure for a scene in Drowning by Numbers, and never took it down when he had finished filming.

Even odder was a pyramid consisting of washing machines. This was, I discovered later, a typical creation of one of the inhabitants of the house, Tim Hunkin. Hunkin makes TV programmes about mechanical inventions - you may have seen the human fax machine in his last Channel 4 series, or his Horrid Dog's Head and Autofrisk on these pages. The washing machines were later replaced by a lift which, since it was erected in the garden, did not take passengers anywhere; but, with the sun gleaming on the waves in the background, it made a spectacular picture.

The pier and pyramid soon disappeared, hidden by the massive promontory which thrusts out over almost the entire width of the saltings. I sat down in the shelter of a tree which could be guaranteed not to blow over - because it already had been - and ate my lunch.

Dug into the sand at the top end of the saltings is a forlorn plough, seemingly left by an over-optimistic farmer who had been seeking a special subsidy for growing corn on sand. Not only was the poor fellow unsuccessful, but he also had to say goodbye to his plough, which is now hemmed in by trees.

I was sheltered from the wind here; but the A12, which had been a dim murmuring in the background, became a roar as it touched the top of the saltings and crossed the bridge. On the other side of the road is the magnificent Holy Trinity Church, which towers over the tiny village of Blythburgh. According to legend, a demonic 'Black Dog' from Hell killed three worshippers and left claw marks in the north door in 1577.

The animals are better behaved there now: I have seen several dogs, not to mention cats, rabbits and the odd horse, dutifully take their places at Holy Trinity for the special service for animals which is held there every year.

Upstream, the Blyth shrinks to a normal, narrow river; but I followed the other bank back towards the sea. It is no wonder that the old railway line was axed; the driver was forced, on pain of two years' imprisonment, to keep his speed down to 16mph, and the guard used to stop it between stations to set snares.

Now that it has stopped for good, the path to Southwold follows the old embankments and cuttings across the marshes and heaths. Among the reed beds is a hide for bird-watchers; among the graffiti on its wall is a claim that five spotted redshanks were spotted by Bill Oddie, comedian and twitcher.

After that, the path dives into the only wooded stretch, known as Deadman's Covert (although it also has one or two more cheerful names). It is guarded by a forbidding sign, erected by the Nature Conservancy Council, stating that the wonderful, sandy cutting ahead is barred to humans - unless they happen to be riding a horse.

I have never met a horse on this bit, although I have been chased away by men in Range Rovers and flat hats. Today those chaps had taken the day off and I was free to venture into the horse-only zone. As evidence, I stuck my rucksack

in the middle of the cutting and took a photograph of it. Should the Council wish to mount a prosecution for trespass, they can have the snapshot as Exhibit A.

With or without the illicit part of the route, you eventually hit a stretch of the road that leads to Walberswick - and another television location, this time for the shots at the beginning and end of East of Ipswich, a drama written by Michael Palin. Here the young hero and heroine had their first and last glimpses of each other from their respective parents' cars. Young Palin used to come to these parts on holiday, and he met his wife on the beach.

Back on the old rail track, the world's least helpful signpost stands next to a gap in the embankment. 'Bridleway', declares one of its arms laconically, without mentioning where it leads. Similarly, the second and third directions are merely 'Bridleway'. The fourth, by way of variation, says 'Footpath'.

The arm pointing straight ahead directs me to the favourite spot of my favourite walk, a wide and crumbled cutting, its sides covered with yellow gorse bushes and riddled with rabbit holes. Southwold is ahead and Walberswick to the right but you'd never guess, cocooned in this hollow which was sliced out of the earth a century ago.

The cutting deposits you in a narrow road which in turn leads, as straight as the railway track it replaced, back to our starting point. The nearer I got to the river, the more the wind recovered its strength.

Today's pedestrians clatter over a modern Bailey bridge. For the film of the doomed love affair, a period- style version was built upstream. But, although the structure was knocked up by carpenters to portray a fiction, the film accidentally unearthed a truth.

It seemed highly artificial: the film of the book of the painting of the bridge. But when The Bridge was released, two of Philip Wilson Steer's great-grandchildren introduced themselves to Margaret Hemingway. The artist, they said, had in fact been involved with a married woman during that summer of 1887 and they were descended from the baby which resulted. The novelist had created not just a work of imagination but of fact as well. Most writers fail to do either.

(Photograph omitted)