Sean Coughlan heads off under the channel

The south of France has long held a special place in the chilly corners of the north European imagination, representing romance, sensuality, a sophisticated playground for the wealthy and an ideal of luxury for the Hello! reader that lurks in all of us.

So telling people you’re going to the south of France for a daytrip is like saying you’re going to a restaurant to eat three puddings. It isn’t just pleasure, it’s downright decadent, probably immoral.

But thanks to a combination of the Channel Tunnel and the French passion for fast trains, you can go deep into Provence, spend a few hours there and still get back to London not long after closing time. Of course it’s expensive - and it’s a long way to go for a brief visit. But if you decide you need an emergency shot of Provenal sun and you’re ready to stick common sense into the pending tray - it can be done.

In this horizon-bro adening spirit, I leave Waterloo Station in London on the 6.19am Eurostar train, travelling first to Paris, where I catch a direct train to Avignon, a beautiful medieval walled town, about 25 miles inland from the Mediterranean.

On a long-distance daytrip, the journey itself has to be part of the pleasure and it helps that the train from Paris is a fast and comfortable TGV (train grande vitesse), which hurtles through the French countryside at 200 miles an hour. Paris to Avignon takes a little over three hours, sweeping through the lush fields of Burgundy, down the Rhone valley and into Provence, where you can see the landscapes that inspired Czanne and Van Gogh.

When the train doors open at Avignon the change to the unmistakable climate and atmosphere of southern Europe is sudden. No matter how high the temperature climbs back home, you never get the same all-enveloping sensation of warmth, the scented, sluggish air of the Mediterranean.

Avignon is in the middle of its annual arts festival, which for the last two weeks in July and the first week in August takes over the town. Hundreds of plays are performed here, with historic buildings, public halls and courtyards turned into makeshift venues for all kinds of classic and experimenta l theatre. It’s a kind of Edinburgh Festival with permanent sunshine and decent food.

The festival creates a tremendous holiday atmosphere, with visitors packing out the town, entertained by street performers and cajoled by leafleters trying to persuade them to see a play. As I’ve less than three hours, I think I should hurry through the crowds to see the major sites - the papal palace, the original Pont d’Avignon, the cathedral - but as soon as I start walking down the main street I realise it’s time to slow down.

The heat is sweltering and I’m still dressed for the London I left behind.There’s an enjoyable sense of having been beamed down, stepping on to the train in the grey south London morning and stepping off into the warmth and languor of southern France. The best way of acclimatising, I decide, is to join the festival-goers sheltering in the shade of a caf.

I choose a place at random, on a winding backstreet away from the crowds, and in one of those weird travel moments, I watch as a crocodile of infant children marches up the road past the caf, holding hands and singing some kind of nursery rhyme at full volume, led by a teacher who is also singing at the top of her voice, chin up, eyes staring straight ahead.Indifferent to passers-by, they disappear over the brow of the hill, their tinny voices remaining audible minutes later, as their song echoes around the stone walls.

Concerned that I might be disappearing into a Jean Renoir film, I slug back the coffee and wander back to the town’s main square, dominated by the Palais des Papes. This Gothic palace was the official papal residence for much of the 14th century, when the popes fled the chaos of Rome to set up a temporary base in Avignon. The town’s walls and much of its more ostentatious architecture date from this period, when the power-brokers of the medieval church were installed here.

If I’d been staying longer I might have taken a tour around the palace, or visited others of the grand buildings in the old town, but instead I spend my time walking, soaking up the atmosphere. I’ve no luggage and I’m carrying nothing heavier than a notebook, so I’m ready to ramble, relishing the sense of having travelled so far in a day.

But it soon passes and I have to sprint for a train that runs non-stop from Avignon back to Paris, and the last train to London, where I arrive at 11.20pm, my face still red from the southern sun.

Eurostar 0345 30 30 30.

Return fares to Avignon start at #163;109