Where do writers get their ideas? Novelists can be vague about what sparks the beginnings of a book - but Daphne du Maurier knew exactly what inspired her finest short story.

She had taken a trip to Torcello, the largely deserted island on the fringes of the Venetian lagoon. While she was having an alfresco lunch in the sunny garden of the Locanda Cipriani (it's still well worth taking the time to make the journey for a meal), du Maurier recalled observing a young couple at a neighbouring table.

'They looked so handsome and beautiful and yet they seemed to have a terrible problem and I watched them with sadness,' the novelist wrote later. 'The young man tried to cheer his wife up but to no avail and it struck me perhaps that their child had died of meningitis.'

A curious intuition, but du Maurier was able to spin this slender observation into literary gold. She named the couple John and Laura Baxter and they became the central characters of Don't Look Now.

For some cities, you need to pack a guidebook. The museums of Paris, for example, or the classical antiquities of Greece will make little sense without the detailed notes of a glossy Dorling Kindersley or a Blue Guide.

For other places, you would do best to take a

Ghostly, beautiful

And nothing quite summons up the ambience of out-of-season Venice as Don't Look Now. In Penguin's du Maurier short stories collection, Don't Look Now runs to fewer than 50 pages, but each time I read them I am effortlessly transported to the deserted backstreets of la Serenissima.

Guidebooks lay out the menu of a place, as it were, but they don't usually tell you what to eat. With a copy of Don't Look Now in your hand, du Maurier can guide you through her Venice. It's a pleasure worth lingering over.

BEFORE we embark on this literary pilgrimage, we need to address the matter of the film version of Don't Look Now. When good fiction is brought to the screen, the results are often dire (The Shipping News, for example). Yet when the filming of Don't Look Now began exactly 30 years ago this year, it was to prove that rare creature: a film that managed to match the quality of the book.

And while films normally cut and compress fiction, Don't Look Now director Nicolas Roeg needed to extend and amplify the original story. So, remarkably, the film and book complement each other - something that du Maurier was happy to acknowledge when she saw a special preview.

There are differences. In the film, John Baxter, played by Donald Sutherland, becomes an agnostic church restorer who travels to Venice with his wife Laura (Julie Christie) after their young daughter had drowned.

In du Maurier's story, as we know, the Baxters' daughter died of meningitis - and John and Laura are simply enjoying a short holiday in Venice.

But the central tale remains mostly intact. The main elements of the story were all observed by du Maurier on her visits to the city. She had seen two sisters, one of them blind, and she had seen what she thought was a little girl in a coat with a pixie hood - the misapprehension that provides the awful twist in the tale.

The plot hinges on a series of episodes linked with clairvoyance and psychic precognition - subjects that fascinated du Maurier.

In a restaurant - on Torcello, of course - John and Laura meet two Scottish sisters, one of whom, named Heather, is blind and clairvoyant. She tells Laura that she has seen her dead daughter sitting at the restaurant between her and John, smiling and happy.

THE blind sister also reveals that the daughter is warning John and Laura not to stay in the city because their lives are in danger. In a series of macabre-twists - the final one being the most terrifying and unforgettable in English literature - the gripping tale is played out against the background of a largely deserted Venice.

With an economy of language, du Maurier subtly brings the city alive. The evening after their lunchtime encounter with the sisters, the Baxters have their

first brush with danger. The novelist paints a vivid picture of the spookiness of night-time Venice familiar to anyone who has visited the city.

On the way to a restaurant, they become lost. 'The canal was narrow, the houses on either side seemed to close in upon it, and in the daytime, with the sun's reflection on the water and the windows of the houses open, bedding upon the balconies, a canary singing in a cage, there had been an impression of warmth, of secluded shelter.

'Now, ill-lit, almost in darkness, the windows of the houses shuttered, the water dank, the scene appeared altogether different, neglected, poor, and the long narrow boats moored in the slippery steps of cellar entrances looked like coffins.'

Du Maurier leaves clues so that you can follow the Baxters through this 'sinister' place, which can be found as described at the back of the San Martino church near the Arsenale.

The real charm of Venice lies in its quiet backwaters. By day, as du Maurier notes, they are perfectly lovely. Follow John and Laura to the Greeks' church, San Giorgio dei Greci (easily located by its drunkenly leaning bell tower), and you will find yourself walking along Fondamenta San Lorenzo.

With a copy of the wonderful Venice For Pleasure by J. G. Links in your grasp, you will learn that it was here that Bellini set his easel to paint Miracle Of The Cross at the Bridge of San Lorenzo almost 500 years ago. Study this view carefully: when you look for the painting later at the Accademia you will see how little Venice has changed. Yet the Venice revealed in Don't Look Now is a very different city from the one seen by most tourists.

Julie Christie recalled the filming with special pleasure: 'Venice had that strange, ghostly emptiness you see in the picture, full of magic and portent, very wet walls, dark alleyways that were damp and glistening. And continual reflections; everywhere you looked there was water.'

Her remarks are an uncanny echo of du Maurier's descriptions. This is John Baxter sheltering from a downpour in St Mark's Square: 'The experts are right, he thought, Venice is sinking. The whole city is slowly dying. One day the tourists will travel here by boat to peer down into the waters, and they will see pillars and columns and marble far, far beneath them, slime and mud uncovering for brief moments a lost underworld of stone.'

The film is at pains to avoid the familiar images of Venice. 'St Mark's Square is not the city of Venice,' said Roeg. 'Venice is a wonderful thing, a work of art which reveals itself slowly, as do all great beauties.'

It is interesting how faithfully the film sticks to the book in its choice of locations. The hotel 'by the Grand Canal' where John and Laura stay in the book is only vaguely described, but on stepping out of it they are quickly on the 'Molo' and heading along the sweeping Riva degli Schiavoni quay that runs from the Doge's Palace to the Biennale Gardens.

Du Maurier may have been thinking of the Gritti Palace, the Europa e Regina or the Luna Baglioni. The film uses the Hotel Gabrielli Sandwirth, a few minutes' walk east along the waterfront from St Mark's Square.

There wasn't enough space in the Gabrielli's rooms to film the interiors. These scenes, including the famous love scene (so raunchy that the film company cut it out for du Maurier's special preview), were filmed in a suite in the Bauer Grunwald, which is on the west side of St Mark's Square. In the film, John Baxter is restoring the 12th Century church of San Nicolo dei Mendicoli. In reality the church was restored by the British Venice in Peril fund in 1973. In Venice For Pleasure, J. G. Links describes the church as 'a miracle of enlightened restoration'.

From Schiavoni you can reach the church by taking a No 2 ferry to Zattere. To the first-time visitor the vaporetto network can look complicated, but it is worth persevering - it really is the only way to see Venice.

Don't Look Now's terrifying climax happens in very similar locations in both book and film. In the book, the action takes place near the canal at the back of the San Martino church. Roeg places the key scenes of the film a short walk away in the Calle di Mezzo, just below the Campo Santa Maria Formosa, with its gorgeous, mildewed wedding-cake church.

This is where John catches sight of the figure in the pixie hood who slips through a large iron gate before disappearing. In reality, the building they enter is the Griman Palace. Once one of the city's most handsome renaissance palaces, famous for its rich frescoes, it seems to have been left derelict for many years. Now, at last, restoration seems to be under way.

In the 30 years since the film was made, Venice has been transformed into one of the most fashionable cities in Europe. The real peril for the city doesn't lie in the ever-rising waters of the lagoon but in its glitzy transformation into an Adriatic Greenwich Village.

Daphne du Maurier would probably have been horrified.

Getting there

British Airways (0845 7733377) offers return flights from Gatwick to Venice with fares from £134. Accommodation at the Europa e Regina starts at £299 (£186). Call Starwood Hotels on 00800 325 35353. Apartments from £475 per week can be booked through Venetian Apartments on 020 8878 1130, or visit www.venice-rentals.com

Destination guide: Italy