Lost tourists are a familiar sight in Venice. You see them blocking the bridges and clogging the calli, eyebrows knitted over maps that defy cartographic logic and are rendered all but useless within Venice's inner tangle of pathways.

“If in doubt, follow a Venetian,” says local tourist lore; advice that has rescued me from many a ramo (blind alley).

Despite numerous visits I'm a repeat offender, but my visit last April was to be different. As Londoners were waking up to marathon day, Venetians were preparing for their annual Su e Zo per i Ponti, or Up and Down the Bridges event. As a participant, I would be following not just one but at least 10,000 locals through the city's out-of-the-way neighbourhoods, via 45 bridges, without having to consult a single map.

Unlike the London Marathon, Venice's race, walk, march, or run, as it's variously called, requires no training. If you are registered and fairly fit, you can just turn up and follow the crowd - a mixed bag of jolly folk groups, schoolchildren, local families, regional bands and participants of all ages from around the world.

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Physical demands aside, the two events share much in spirit. Su e Zo was conceived 30 years ago as a non-competitive event in which families and groups from Venice and the Veneto region march together in friendship and solidarity while raising money for charity. It's an important event in the busy Venetian calendar.

One local delighted in showing me the family album, with pages of 1970s snaps depicting mum, dad and kids posing by various bridges in a fine selection of flares.

For visitors the walk offers the chance to mingle with locals at what is a traditional and fun event - and explore a large area of Venice without getting lost.

Festivities kick off with a Mass and a short warm-up in St Mark's Square, although the event began for me the previous night with the impromptu performance of an improvvisando choir from Conegliano. Their melodic midnight gathering in St Mark's Square marked the start of the Su e Zo festivities, and the same choir was singing at the Holy Mass of Su e Zo per i Ponti in the Basilica San Marco.

Next morning at 8am I skirt the front of the famous landmark and duck through a heavily embellished sidedoor. I'm about as Catholic as I am an early Sunday-morning riser, but today I have an invitation of sorts, and I'm sure He will turn a blind eye. As the dulcet-toned choir thrills the congregation, I gorge on the sumptuous interior, deliciously uninterrupted, for an entire hour. This is the way to see the Basilica.

Mass over, I head off to join local group, 40xVenezia. All 130 of us, including three Britons and an American, wear matching T-shirts except for the kids. Their T-shirts depict a cartoon-sized foot stepping in something nasty, alongside the words: Attenzione: cacca.

“Yes, cacca,” confirms the group leader. “That's what every Venetian mummy worries about.” There's cold comfort in knowing that dogs poop, even in Venice. By the time we reach the huge inflatable starting arch by the Doge's Palace, the tranquil square of two hours ago has vanished under a sea of banners, feathered Tyrolean hats, marching bands and flag-wavers, children in national dress and thousands of Italians clad in alarmingly sporty-looking Lycra.

Flags are hoisted, the official beacon is lit and ... we're off. Only we're not because there are about 9,000 people ahead. Having chosen an untimely moment to dash off and snap some flamboyant sbandieratori (men in tights), I've become separated from 40xVenezia's team leader. He texts me from the Bridge of Sighs. “This is only bridge number one,” he scolds when I catch up with him.

The route winds its way through six of Venice's seven sestieri, or districts - a three-mile route crossing 32 bridges and a longer five-mile option crossing 45. But it's just as easy to plot the route by its churches - I later count 22 on the longer walk, including the magnificent Gothic San Giovanni e Paulo. But although it encompasses all the main sights in Venice the spirit of Su e Zo defies tick lists.

There is far too much chatting going on for that. Leaving the well-trod Riva degli Schiavoni, Venice's most popular waterfront, we enter the working-class Castello, skirting the tall, embattled walls of the Arsenale - once the naval epicentre of Europe and the true seat of the republic's wealth.

Trooping eastwards along the Fondamente Nuove, crossing the “scandal bridge” - six years in restoration, according to fellow walkers - we enter a tranquil residential neighbourhood in the alluringly melancholic district of Cannaregio, home to the world's oldest ghetto. What the residents throwing open their shutters think on seeing the charge of the 10,000 below can only be imagined.

We pass a couple optimistically walking their dogs against the pedestrian tide, and I chortle as the familiar call of “A destra, a destra!” - a request to tourists to keep right - is politely ignored.

Gridlock occurs at numerous points, particularly on the smaller bridges, but volunteer marshals help to steer us onwards - “Avanti, avanti!” - and create mini-diversions where necessary. An hour in we stop briefly in a leafy campo dotted with the guild inscriptions of tailors and weavers, under the shadow of the imposing Chiesa dei Gesuiti. This is the first of three official refreshment points serving free tea, water and brioche.

Anglo-Saxon queueing sensibilities have no place at Italian free-for-alls and in the scrum I meet Beryl Burne, a pensioner from Sutton, back for her fourth walk. “I make more friends at Su e Zo than on all my other visits here,” she tells me. “You get to see the real Venice, both good and bad - the residential areas, the graffiti, not just the touristy bits.”

Crossing the Rialto Bridge, we enter the workaday San Polo district, its labyrinthine mercantile streets heaving with osterie e bacari, taverns honouring that noble Venetian vocation of good fare.

In contrast are the relatively airy, residential streets of neighbouring Dorsoduro, where we begin the home straight along the broad Venetian promenade known as the Zattere, flanked by former salt warehouses, churches and classy restaurants that take in the Giudecca, across the eponymous canal. Soon we're crossing the Accademia Bridge and heading back into San Marco for the finish.

One of the runners has completed the course in 50 minutes; we've walked it in just under three hours. Souvenir medals are generously awarded to all participants, but 40xVenezia has won a major prize for the most Venetian participants in a group, and we troop off to the prize-giving stage to collect a comically large Murano wine glass trophy, promptly christened with Bellini. I'm celebrating (bar a little false start) three entire hours of not getting lost in Venice - and the fact that my shoes are cacca-free.

Further information

The next Su e Zo per i Ponti is on April 19. To register visit www.tgseurogroup.it/suezo/en. It costs €4.

For public transport to Piazza San Marco visit www.hellovenezia.it. A combined return ACTV vaporetto and Su e Zo ticket costs €6 (a single vaporetto journey is usually €6.50).

Stay

For information on hotels visit www.veneziasi.it.

Getting there

Ryanair flies to Treviso, near Venice (www.ryanair.com).

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