In a city which dreamed up a five-storey mechanical elephant to stalk its quays like a benign, urban King Kong, anything is possible. That city is Nantes, and the 21st century mammoth has become not only its emblem and prime attraction but a shining example of how art and imagination can regenerate a dying city.

The former industrial capital of Brittany, dubbed “the loopiest city in France” by The Sunday Times, is far removed from the Brittany of picture postcards. Devoid of charming, rocky coves, the once-powerful port built its fortunes on slave-trading, shipbuilding and food processing.

When the river silted up and manufacturing moved out, a seriously creative vision was required to transform defunct factories and shipyards into pleasure palaces worthy of the tourist euro.

These include a beautiful Art Nouveau biscuit factory now home to bars, galleries and a hammam, an exquisite botanical garden awash in fanciful sculptures and the animatronics workshop which kickstarted the revival of Nantes 11 years ago by bringing that elephant to life.

But the biggest event of the year is Le Voyage a Nantes, which draws some half a million visitors to the city in July and August.

It’s named for and inspired by the great imagineer Jules Verne, born and raised in the city. This culturefest gets more ambitious every year, with many eye-popping pieces of public art retained from previous festivals and new sculptures and installations added every summer.

They include an exterior slide attached to the wall of the 300-year-old moated castle, allowing visitors to speed around joyously, and a series of giant rings lighting up the quayside of an island which once housed shipyards and warehouses.

There are also surreal outdoor ping pong tables which allow six players to compete and a children’s playground resembling the cratered surface of the moon.

This year’s new works, on show from June 30, will include a ghostly crystal and neon skeleton floating above the orchestra pit of the Graslin theatre, an immersive work by James Turrell at the newly-extended museum of modern art and a dizzying urban jungle perfectly in tune with a city determined to be green in every way.

In fact Nantes Tourism’s most ingenious creation is the 10-mile green line which links everything worth seeing; follow the line clearly painted on the pavement and you won’t miss a thing.

You don’t need to wait for Le Voyage to enjoy Nantes, full of things to see and do year-round. They include Les Machines de l’Ile, whose creators followed up the giant elephant — which offers rides to 49 people several times a day — with a wonderfully fantastical carousel in which horses are replaced by marine creatures and boats.

There are also workshops where visitors can see the giant spider, ant and flapping birds destined to be marching amongst visitors within five years, perched on the branches of a giant “heron tree” on the mainland shore.

And the town’s Michelin-starred restaurant, L’Atlantide, will be a great vantage point for this new animatronic wonder — and is already unmissable for foodies.

In its thrilling clifftop location overlooking the island, chef Jean-Yves Gueho does full justice to Brittany’s excellent fresh fish, vegetables and the buttery Breton baked delights which are the best in the whole of France.

Dining out, the city’s choices are mouth-watering; there’s a good choice of fish and vegetable dishes at Bistronome Nantais, an elegant indoor-outdoor restaurant facing the Cathedral, while Le Bouchon, in one of the medieval half-timbered houses lining the back streets behind the Hotel La Perouse, is an atmospheric dining spot.

From La Perouse, with its own wonderful breakfast, it’s easy to walk through the hilly but largely pedestrianised Graslin quarter leading up to the synagogue, full of elegant squares and 18th century buildings.

Nantes’ long Jewish history dates back to the 11th century; it was the first port of call for many Spanish and Portuguese Jews fleeing the Inquisition, and a community depleted by the Holocaust has been restored by an influx of North African Jews who have transformed the handsome synagogue built for Ashkenazis into a house of mostly Sephardic worship.

There’s a full programme of events in an adjacent cultural centre, where kosher food is dispensed from a shop twice a week.

A plaque commemorating the city’s Holocaust victims sits beside the war memorial, itself on the main boulevard named for the 50 hostages the Nazis took in reprisal for a Resistance effort.

Nearby the covered market of Talensac is one source of that famous butter, from the Beillevaire dairy, whose stall here is staffed by Bretons in typical striped tops and berets, while local cheeses sit alongside butter bursting with rock crystals or flavoured with three different peppers.

Or sample the finest of all French pastries, the impossibly buttery Kouign Amann in the fabulously ornate La Cigale brasserie, five minutes from the synagogue and opposite the opera house. Close by, there’s retail therapy on all three floors of the equally elegant Passage Pommeraye, a covered Parisian-style shopping arcade.

While the city centre is very walkable, trams make it easy to venture into Nantes’s diverse neighbourhoods. There is even a frequent water-bus service to sleepy Trentemoult, a charming boho suburb on the far side of the river whose colourful houses are worth a quiet stroll if this visually exciting city occasionally feels too frenetic.

Because with the world’s first 3D-printed house newly opened in Nantes, there’s no stopping this endlessly innovative corner of France.