It is not a secret rave expedition, under cover of the night and out of sight of the law but it might be as the rain whips into the windscreen and our car bounces off the bog beneath the tarmacadam on a narrow mountain road to only God knows where.

On the first, rainswept night of the New Year, here be a mystery trail as we're bound, not for some irregular rave rendezvous, but Donegal's own magical heart of darkness. Six miles behind us is the slippery and elastic concept and state of mind known as Gweedore. Ahead, where golden and white-tailed eagles once flew, lies one of Ireland's most bleak mountain roads to the sanctuary of Letterkenny. Our destination: the Cois Laoi centre in Dunlewy at the head of the Poison Glen. The attraction, playing the first night of 1994 in their North-Western spiritual home: Altan.

Of course, the six members of Altan hail from all over Ireland; only singer and fiddler, Mairiad Nm Mhaonaigh was born and bred in Gweedore. But geographical and genealogical accuracy must needs submit to art since it's from Gweedore and its environs that Altan derive their inspiration and the core of their repertoire.

1993 was a very good year for Altan. Following the Chieftains, the Seventies witnessed the emergence of a platoon of Irish music "supergroups": Planxty, The Bothy Band, Clannad, De Danann and Moving Hearts. But in the next decade, the tide ebbed. Only recently have Altan been recognised in Ireland as the leaders of a second wave.

Qualify that: the cognoscenti always knew. But only in the past year has Altan's reputation begun to percolate beyond the tightly policed borders of the traditional world as they played BBC2's The Late Show and gained accolades from Q and The New York Times. Moreover, on the night Altan released their latest album, Island Angel, The Rolling Stones, on their Dublin sojourn, mitched away from the sanctum of Lillie's Bordello to join an afterhours, post-reception session in a hostelry I can hardly mention. And yet as in most tales of traditional music, the Altan phenomenon is a slow-burning not a brushfire story.

At its centre are Nm Mhaonaigh and her husband, flautist Frankie Kennedy. Mairiad's father, Francie is a teacher and fiddler in Gweedore and the teenage Frankie met the family on Donegal holidays to learn Irish and play music. Both became trainee teachers and first recorded in 1979 on an album by the singer, Albert Fry.

Married in 1981, their first group Ragairne which included Enya, recorded an album Ceol Aduaigh, belatedly released in '83 by Gael Linn. But teaching took precedence and only in 1987 did they take leave of absence to form Altan, whose first eponymous album was produced by Donal Lunny.

Signed to the Connecticut-based label, Green Linnet, Altan became passage migrants, essentially summering and touring in America, a policy that may have served to delay the expansion of their Irish audience outside traditional true believers. But if the seeds of their music were slow to flower on Irish soil, they bloomed abroad.

The Red Crow and Harvest Storm, their two albums between their debut and the latest, Island Angel, both won the American indie NAIRD awards. But let's not tediously calibrate another Irish music business story. Instead I'm in Donegal because Altan's music reflects and celebrates the vibrancy of their own community.

The vitality not the fragility's since The Poor Mouth image of traditional music should now be cast aside as a disservice. Through my Sixties youth, I recall that beggared image, as the tradition got inextricably connected with grinding backward rural poverty. RTE features on emigration invariably featured a sequence with the bittern's note of a keening pipe lament.

The tradition got personified as an auld gap-toothed rustic in a shiny Cleary's suit, bought for the 1932 Eucharistic Congress, that self-same figure typecast to beachcomb amid the debris and the dulaman of the Brave New Ireland. Christian Brothers teachers force-feeding the First Language probably didn't help much either.

Gweedore and Altan far from fit that image. Here the past and the future, the fiddle and the lap-top are allies not irreconcilable enemies. Open the door to the Cois Laoi centre in Dunlewy and you'll learn that smartly.

Later Mairiad will explain the first row: "It was full of these little girls who play fiddles and flutes. There was one there asking Frankie what sort of flute should she buy."

Her anecdote is symptomatic of the mood of mutual pride. This isn't like a Dublin night when scattered atoms temporarily coalesce to be entertained. For all their superior virtuosity, Altan become the community expressing itself.

You feel it in the quality of the audience's attention whenever Mairiad sings, a strangely palpable if paradoxical psychic energy where you can hear the quiet and Dunlewy listening. And yet the night is never less than good-humoured, for Frankie Kennedy will always see to the craic.

He'll quip about "bouzoukis made from wardrobes" or embroiders his intro to a Rathlin Island wedding song with a remark about how the gathering of the clans will include the McCartneys from the Mull of Kintyre. And then he'll launch into his own cameo, a slow Armagh air with a passing resemblance to 'My Lagan Love' that has a depth and weight of tone you'll rarely hear from flute players.

And here in this small hall, Altan's own ensemble playing seems to have a bite and charge even beyond their albums. Altan don't so much cruise at altitude as chase the jetstream, as Frankie and Mairiad are flanked by their boxman, Dermot Byrne, and their other fiddler, Ciaran Tourish while at the bookends of the stage, guitarist, Mark Kelly and bouzouki player, Ciaran Curran fill in the lower registers.

Afterwards there's no garlic mushrooms but more conviviality than you'd find in a month of Dublin receptions. Mairiad's father complains about the fishing laws, there's emissaries from the Lunny and O'Bhraonain clans and, introduced to Ciaran Tourish, I enthuse that they really should record a live album and video in Cois Laoi.

We drive back to Gweedore on the same road as on the Clannad 'In A Lifetime' video. I only remotely remember a conversation in the hotel with Mairiad about the 20 different accents of Donegal (according to her) and the 12 different accents of Dublin (according to David Norris) that somehow speedily digresses to Daniel O'Donnell.

Next day, we're going north-east to Culdaff in Inishowen. But, this being Donegal, south-west by Kincasslagh.

But let's linger in Gweedore. Next morning, the Atlantic rains have washed it clean as a tin whistle on one of those sharply refreshing, sunny mornings when the purified oxygen literally rinses the brain-cells.

Gweedore is a state of mind, a townland not a town, with a compact centre and its shops, hotels and restaurants, scattered like a necklace down two miles of its main road. Yet even the most sympathetic incomer can look for the primitive. You grumble that it won't have a Bank Link for those short-changed on a Sunday morning when, of course, AIB have handily provided one.

But any Gweedore story must have its Clannad digression. 'Harry's Game' signalled a change in the Irish psyche. In a peculiar, roundabout way, Clannad and Enya are the futurists of Irish music, entering the 21st century by being simultaneously global and local, fusing technology with the songs and language of the 19th and earlier.

They and now Altan have become significant role-models. Mairiad can backtrack to her youth when less than a handful of families, hers and the O'Bhraonains included, played Irish music. "But now," she continues, "if my father could take seven nights a week teaching music, he'd have a full class. All of a sudden, there's an interest. If they see us, Enya or Maire doing well, they think there's an opening there. It's accessible to do well in this area."

And as Ciaran Tourish points out: "Traditional music ceases to be seen as square and conservative."

But music isn't Gweedore's only asset. As a former teacher from a teaching family, Mairiad understands the importance of education here. Never underestimate Tir Chonaill: "There's a lot of young people here. It's a densely populated area. It has that city thing without being a city because it's all scattered. It's a great place to be brought up in because you're not isolated from the world. Actually because you're so far away, you make an extra effort to be in tune to what's happening in Dublin, London and New York.

"Besides there's a lot of comings and goings between those places. So in its own way, it can be as cosmopolitan as Dublin, hand in hand with its own culture. To me, it's a good proof that the language and the culture can live in a future society."

Donegal people have uncommonly good manners that owe nothing to any socialite's manual on etiquette but they do sometimes grumble about the country's isolation which has been exacerbated by the Troubles. Belfast Protestants who once happily holidayed here have become more cautious; Southerners get squeamish about driving through the border-checks on the A5 from Aughnacloy to Derry.

And yet that isolation keeps Donegal comparatively unspoilt. Back in Dublin, I meet Liam O'Maonlai and we discuss the differences between Gweedore and the Connemara and Dun Chaoin Gaeltachts. Liam, who guested on Harvest Storm, says about Donegal: "You've got to be a pilgrim to go there."

So this pilgrim goes west to Kincasslagh, my excuse a lunchtime session in Iggy's Bar that Altan want to catch. And really, this explains the difference between trad and rock, however indie and alternative the latter might claim to be.

Rock acts don't, indeed can't, casually drop in on lunchtime sessions to play when they're touring whereas for Altan and their similarly afflicted colleagues, it's as natural as the sun crossing the sky.

Of course, we get delayed. There's an unsuccessful attempt to meet an early-rising Mary Coughlan band who also played Gweedore last night. Then, in one of those regular rural coincidences, we bump into Maire Nm Bhraonain's husband, Tim Jarvis, at a crossroads and detour to the family bar, Leo's Tavern for a jorum. By the time we reach Kincasslagh, Altan have moved on.

Not that it necessarily matters. In the tightly-packed bar, what looks like a never-ending session is simmering on. There's a litany of Lunnys, Donal and his brothers, Manus and Phelim, four fiddlers plus a supporting cast of six other musicians, playing so single-mindedly that they don]t seem to notice their glasses are empty.

Meanwhile, a friend peers inquiringly at a photo over the bar. "Who's that playing the trumpet?" "It's Gay Byrne." "He isn't really playing the trumpet." The riposte is conclusive: "Why not ask him yourself, he'll be in in a minute."

On the opposite wall hangs a portrait of another Donegal celebrity, the late fiddler, John Doherty. A woman starts singing a slow air. It sounds authentically trad so I'm dumbfounded to identify it as 'The Rose' by Mick Jagger's old sidekick, Bette Midler.

But then, the tradition is neither pure nor polluted. Next day, we're talking about the relationship between Irish and world music when unprompted, Mairiad enlists John Doherty in her argument:

"I feel if all the old musicians had the access, the CDs that we have, they would be playing it. Because they had no restrictions. They played any tune they heard, military band tunes, stuff from travelling circuses, anything that they enjoyed. One of our sources is Con Cassidy and one of his favourite tunes is 'The Marseillaise' and he plays it like a traditional tune."

But then Irish music has always had its importations like the hornpipe. "But you know what happens then," explains Mairiad. "It was imported in but then the Irish composed tunes based on that rhythm and put their own accent on it."

Eventually, we make it to Culdaff, close to the tip of the Inishowen peninsula and Malin Head, the most northerly point on the island. Our venue, McGrory's is the local hotel. Behind the stage, there's old shop-signs from when McGrory & Co. was the local store, selling 'Grocery, drapery and Boots'.

But again, the past and the future fuse rather than collide. McGrory's must be the only Irish hotel which boasts a 16-track recording studio. Anyone looking to demo away from the distractions of Dublin can profitably contact John and Neil McGrory at Forge Brae.

This is also the territory of Altan's other fiddler, Ciaran Tourish, a Buncrana man, Dunlewy was Frankie and Mairiad's homecoming; tonight is his. But on the second set of tunes, a string breaks and a somewhat abashed Tourish has to trundle through the crowd before carrying out running repairs.

That's the lone hiccup. Altan's music just has an incredible joie de vivre. Over the years, different bands have specialised in different sounds and though box-player, Dermot Byrne, now has a more influential role, the core of Altan is the trio of the two fiddlers and Kennedy's flute.

That gives them their special melodic buoyancy. Altan can attack and accelerate into the jigs and reels with the best of them but they never forfeit a certain airiness and lightness of touch. It's almost like bouncing down one of those Donegal mountain bog roads when the car hits hump and almost takes off - but Altan have higher gifts of levitation.

They've also become leaders of a new generation. Indeed, I'm beginning to suspect that, unbeknownst to the Dublin media, we may have entered a new phase of traditional revival. But how do Altan see themselves compared to their predecessors?

"When we started playing," recalls Mairiad, "it was very hard to get good music. There was a void but then The Bothy Band, De Danann and all those started and it was great because it reinforced someone like me who was just scratching away at home."

Frankie weighs in: "What I think what all those bands and Planxty did was take Irish music and put together different arrangements, some of them very intricate. All of those groups had their distinct sound and it was always going to be very difficult to follow them.

"There was a period there when nobody was coming up with anything distinctly different. In the last few years, I think the time is ripe again. For example what Sharon's doing is quite different because it's based on just the accordion and the double-basss and then she's playing some Irish stuff and some non-Irish stuff.

"Now what we're doing is bringing a repertoire that hadn't been really tapped before. And if you're playing traditional music, it's a great help if you're playing tunes that people haven't heard before. In other words, we weren't regurgitating what De Danann or The Bothy Band did."

If less so than before, Irish music can still be weighted down by all manner of unappealing cultural baggage, all those associations of poverty, emigration and general backwardness. Mairiad thinks that paradoxically their initial American success happened because their US audiences did listen without prejudice.

"In America, people don't have those preconceptions or associations with the sadness of emigration. They don't have restrictions, they just accept the music for what it is."

Like many an Irish musician, Frankie confesses that "We would be more apprehensive about playing before an Irish-American audience than just an American audience."

Ciaran interjects: "The Irish-American audience would be asking for 'The Fields Of Athenry', 'Four Green Fields', 'The Town I Loved So Well', all this crack."

Frankie recalls a date from three years ago before an essentially Irish-American audience in Iowa: "In the middle of the first number, we realised 'whoops, these people came expecting something else.' Now they were great by the end of the night but we had to work really hard. Then at the end of the night, you have this oul fellow telling us we didn't sing any Irish songs. So we explained to him that singing the old songs and singing in Gaelic was slightly more Irish than the songs he was talking about."

Frankie's punchline: "So then he rounded on us and asked us what had we done with the country since he left it."

Earlier, Mairiad had been talking on a mobile phone to Sharon Shannon, herself in the middle of 'The Woman's Heart' tour. I tell her about women rock friends who are slightly envious about the acceptance and prominence of women in traditional music. Mairiad's response is to remind me that this wasn't always the case:

"Up until this century, women as musicians were out because of the childbearing. So most women who were recorded were concertina players because it was a womanly instrument. There were a few pipers but very, very rare.

"So when you got married, it was 'forget about it' because you had to stay at home and mind the children. So the balance was wrong. Women were regarded in the tradition as those who taught the songs to the children . . . Like when I started playing the fiddle, I remember going down to Glencolumbcille and this man was playing the fiddle, a wild eccentric, and he said to me 'And you married and you're playing the fiddle!' Almost to say 'Does he let you out to play the fiddle'. The older ones would think like that and find it very odd that I was playing."

History changes, also geography. Gweedore people seem to turn up everywhere, these days. Mairiad laughs about a local Jesuit, now exiled in Tokyo who's teaching Irish to the Japanese Empress. And as she tells it, East can meet West in the oddest places.

"We were up in Maine on American Independence Day and we were at a barbecue on the beach and this man comes up and greets us in Irish. So I say, great, he's one of us. But he says no, I'm Hugh Curran, a Zen Buddhist from Gortahork."

But as always, Frankie gets the last word: "The only guy from Gortahork I ever saw with a mantra, it was an Opel."