So the reminders that San Sebastian is said to be an ETA power base . . . graffiti telling tourists that they're not in Spain, for example, or sinister collecting tins in the bars of Calle Bilbao . . . are a little shocking. Yet most Basques will tell you that while proud of their otherness, they do not condone violence. They prefer instead, they say, to let their Basque identity find expression through gentler means . . . language, art and cuisine.

Especially cuisine.

Earlier this year a team of international food critics drew up a list of the 50 best restaurants in the world. Three in the top 30 are in San Sebastian. That's quite an achievement for a town of just 200,000 people.

Superchefs Martin Berasategui is one of the triumvirate of San Sebastian's superchefs. With three Michelin stars and a reputation as a pioneer of "progressive Basque" cuisine, his restaurant just outside San Sebastian came in at number 27. It's a surprisingly low-key place, where the tables look out over a beautiful rural scene, despite the restaurant's proximity, in the other direction, to blocks of flats.

Berasategui himself, who is squat with an efficient manner, thinks he knows why Basque cuisine is increasingly thought to be among the best in the world.

"People here grow up with food at the forefront of their minds, " he tells me.

"They live for it. They treat restaurants with the greatest of respect, like other people might treat museums. And we have in the Basque Country the finest-quality ingredients you can find."

Eleven or 12 courses in to Berasategui's 15-course tasting menu, I'm getting complacent. The sea-urchin custard with coffee, cinnamon and curry cream had, a few courses back, astonished me with its Dali-esque appearance and equally surreal storm of flavours. So had the squid soup with squid-ink ravioli and squid crouton.

Now finishing a delicate piece of roast sea bass before moving on to the pigeon course, I find myself looking ahead to the "yoghurt liquid bubble" . . . one of three desserts . . . and only slightly surprised to see that it comes with "mist of gentian" and "crunchy flowers".

I have in the space of a couple of hours experienced as many flavours as I might normally expect to taste in a month. I've also become mildly drunk. The attentive sommelier has offered a glass of a new wine with more or less every course. Each is exceptional. In hushed and reverent tones I have been served 2006 Vina Mein from Galicia, a 2002 Vallegarcia Viognier, a 2005 Erial and several others. Unsure of the etiquette, I've followed my heart and sunk the lot. If I've done the wrong thing, the staff are too polite to let it show.

So by the time Berasategui emerges from the kitchen to polite applause from his diners, I realise it's time to find my way home. As I get up to leave I watch the great chef stroll from table to table shaking hands, smiling indulgently. He is the virtuoso conductor, we the transported audience.

There are two diving platforms anchored off San Sebastian's Playa de la Concha, a magnificent curve of sand framed by the thickly forested Monte Igeldo and Monte Urgull. The next morning I am forced to swim from one platform to the other through the choppy sea because it's the only way I can find to work up an appetite for the next phase of my research.

The previous evening's blow-out would, I was assured, seem a light snack compared with what I would be served at the sidreria, which was to be my next dinnerdate. Ignoring the other local restaurants in the top 50 . . . Arzak and Mugaritz . . . I'm keen to explore the opposite end of the local culinary spectrum.

Cider-house restaurants Sidrerias, in striking contrast with the likes of Arzak and Berasategui's, serve Basque cooking at its simplest. They are cider-house restaurants where diners top up their glasses from enormous barrels, drinking as much of the delicious scrumpy as they like.

The form is to take it little and often, knocking back each small glassful in one go. I watch the other occupants of the long oak table at Petritegi's sidreria till I'm confident I'm doing it right.

Petritegi's is a noisy, barn-like place where there is no menu. The dishes are slammed down in front of me in quick succession: chorizo slices, cod omelette, fried cod, beef steak, local cheese, quince marmalade and walnuts.

It's man-food. My fellow diners, almost all men, clutch their knives and forks in clenched fists, scooping the food into their mouths in a continuous action. Cider is knocked back with equal skill. Queues form at the taps of the barrels. It brings to mind a feast scene from the Asterix books.

Though the food is cooked simply . . .almost unmolested in any way . . . it's exquisite. The steak is the best I've tasted anywhere in the world. It's very rare, though. In fact, "rare" doesn't quite do it justice: it's as if the cow lingered under a patio heater. But it's somehow perfect.

The cheese and quince marmalade is so good that I'm forced to finish the lot. It is, frankly, a Herculean effort. The cider helps, I find, and my trips to the great barrels become ever more frequent. And so, again, I find myself lurching into a starry Basque night, the worse for wear, in search of a cab.

I'm soon ploughing between the diving platforms again, training for another evening of painstaking investigation.

Tonight it's pintxos, pronounced "pinchos". Pintxos, more than Michelin stars or cider houses, have made San Sebastian's food famous. They constitute the Basque version of tapas, each just a mouthful, and they are piled between the beer taps of almost every bar in town.

In the old quarter . . . the Parte Vieja . . .there are several pintxos bars on every narrow, graceful street. The procedure is simple and, to those who don't speak Spanish, helpful. One simply takes pintxos from the bar while ordering a drink . . . a glass of cold red Rioja, perhaps, or Txacoli, a slightly bitter young white wine which is poured from a height . . . confident that the barman will keep a tally of what you owe.

Pintxos at their simplest are chorizo pieces, pepper, olive and anchovy kebabs, dressed crab on little squares of fresh bread, or freshly fried prawns. Some pintxos bars are a little more exotic, such as La Cuchara de San Telmo, where they specialise in foie gras and squid. Even here, though, no single dish costs more than a euro or two.

Strolling from pintxos bar to pintxos bar through the noisy streets of the Parte Viejo is one of the great European experiences. You will not find a glass of house wine you do not like. You will not fail to be impressed by the sheer quality of the food. Pintxos are, to me, San Sebastian's finest contribution to world cuisine, in part because of the manner in which they are consumed.

Living beautifully I strike up conversations in every bar I visit. I see . . . through a mist of cigarette smoke . . . children chasing each other around a forest of patrons' legs. Perhaps best of all, I'm encouraged to explore the labyrinthine back-streets of what is, beyond doubt, one of the region's most striking cities.

San Sebastian is redolent of old-world European charm . . . a time of living beautifully. It's not surprising, perhaps, if this town stirs pride in its residents; alongside Bilbao, it's a cultural capital to rival those of small, but established, nations.

The profound seriousness of the Basque approach to food is inspiring. Take it seriously, even if to do so leaves you dangerously over-fed, and you will be rewarded not just with exceptional food, but with a sense of what it is to be Basque, too.

GETTING THERE

Getting there Regular flights to nearby Bilbao from Dublin with Ryanair. www. ryanair. com

Staying there Pension Bellas Artes, Calle Urbieta 64 (www. pension-bellasartes. com). Doubles start at 55, room only.

Eating and drinking there The tasting menu at Martin Berasategui's (www. martinberasategui.com) costs 178, excluding wine.

More information San Sebastian Tourist Office: 00 34 943 48 11 66; www. donostia. org