The first thing you must realise about a literary tour of Ireland is that writers are strewn across every trail like chewing gum at a pop concert: you pick one up on your boot every step you take. We all can name half-a-dozen: Shaw, O'Casey, Yeats, Synge, Joyce, Beckett - but just one quarter fold of the Irish Tourist Board's literary map records 75 authors. So keep your head and pick a handful to go with the scenery.

It was taking a gander at the statue of CS Lewis (The Lion, The Witch And The Wardrobe) in Belfast that made me decide to get out of that town in a hurry: "C S Lewis, Ulsterman Writer, Scholar Teacher Christian, Born 1898, Reborn 1931." Reborn is probably a poetic way of marking when he emerged as a creative writer, I suggested innocently to my Ulster guide. "No it isn't," he said.

Fearing I might find similar pious tags attached to Brian Moore, Robert Lynd, St John Ervine and even Michael Longley or Derek Mahon, I got out of town (despite the fine Asian cooking by a Dubliner at the McCausland hotel), and headed for a blacksmith's forge at Hillhead, Co Antrim, which is Seamus Heaney country. I was seeking elucidation of one of Heaney's more cryptic statements, the opening line to The Forge: "All I know is a door into the darkness."

Barney Devlin, the son of Heaney's blacksmith, a man with the commitment of never allowing alcohol to pass his lips but possessing a powerful will to see others gargle, cracked this metaphysical nut with an anvil-like blow. "That's all he ever saw of the forge - a door into the darkness. My father was a cross man and he never allowed Heaney to set foot in the forge."

Then on to the true object of my entire visit: to gaze with admiring sorrow on the birthplace of one of the greatest comic writers of the last century, Flann O'Brien (Brian O'Nolan). Flann, or as we knew him in Dublin, Myles (from his Myles na Gopaleen column in the Irish Times) was to us the quintessential Dubliner: bolshie, literate, witty, often well-oiled, temperamentally anti-authority. He once threw Eamon De Valera's prestigious Institute of Advanced studies into a panic by accusing it of trying to claim there were two St Patricks.

The one flaw in Myles's Dublinosity is that he was actually an Ulsterman, born in Strabane, Co Tyrone, to a family of scholarly distinction (a maternal uncle is still fondly referred to as "the alcoholic musical genius") and only headed south in college days. Not many Dubliners know this, nor want to know. But to my indignation, virtually nobody in Strabane wants to know either. O'Brien is not the literary hero of Strabane; the canonisation, to be rude, goes to Cecil Frances Alexander (1818-1895) author of All Things Bright And Beautiful. The locals get testy when you point out that she definitely was born and raised in Dublin.

Brian O'Nolan's birthplace at 17 Bowling Green Square is a locked, downcast, three-storey terraced house in moulting, milky green; the lace curtains suggest cobwebs and the dour, drawn brown drapes speak of furtivity. It would pass more suitably as the birthplace of Bram Stoker (b Dublin 1847). True, they have named a housing estate after Myles, but a note of celebration somehow does not rise easily from a housing estate.

Bowling Green House faced it across the square. I wanted to know how many B&B customers rented this ideal vantage point to bear melancholic vigil to Myles/Brian/Flann. According to the lady of the house, one guest mentioned him once at breakfast.

But suddenly a ghostly connection was made. One of Myles' great characters is The Brother, the man who was an expert on everything from war to landladies' rheumatism. Suddenly the landlady said: "Of course, the Brother comes up from time to time." The Brother! What a shock! Did literary characters have ghosts? But it was the real brother, Michael, she was referring to, behaving in a fashion that anyone who knew The Brother would recognise. Watchful, dabbling in mysterious assignments.

On we went to Donegal town. I chose this because when you are at the literary lark, you should do your homework, and there is no denser homework in Ireland than the Annals of the Four Masters. It was compiled by a Franciscan monk, Michael O'Clery, with three other Masters, and covers a period from earliest times to 1616. The Annals tell of battles, murder and war. They began writing in 1635, having travelled the country for three years. It was a timely endeavour because soon Cromwell (d 1658) and the Williamite wars were to torch the majority of Ireland's ancient manuscripts. Only skeleton ruins of the old friary where the Masters worked remains.

You will be wondering what the scenery was like along the road from Belfast to Donegal. Nice, so far as I know, because these were talking journeys, refreshed at one point by a visit to my guide's own B&B, Laurel Villa, a Victorian townhouse in Magherafelt, Co Derry. It is distinguished by its display of ancient medical bottles, relics of a doctor's surgery that serve as some kind of message to over-indulging guests, I suppose.

But now I shipped out alone in a Bus Eireann coach to Galway by way of Sligo. (You could drop in on Yeats country outside Sligo, if you like.) At Galway, a new guide took over and we headed out for Ireland's equivalent of an Red Indian reservation, the Gaeltacht at Spiddal, where the government subsidises communities to live "through the medium" of Irish. But the commitment to the language is genuine and healthy. Gaelic speakers can be a tough bunch and very independent-minded. Which brings me to two characters you never knew you wanted to know about: Mairtin O'Cadhain. (1906-1970), and Blind Raftery, the early 19th-century poet and fiddler.

In the 1930s, O'Cadhain was principal of the two-teacher Gaelic school at Carnmore (now a six-teacher school) and was endlessly in trouble. His most famous work, Creé na Cille (The Churchyard Clay), a comic novel where residents discuss their lives and grudges, no doubt drew on contemporary material. Fired by the Paris priest in 1937, he was too much of a republican even for President De Valera who interned him during what southern Ireland officially referred to as The Emergency (second world war). But Ireland has a way of accommodating its rebels, and he ended up Professor of Irish at Trinity College.

Then on to the beautifully unmanicured cemetery of Killeeneen, Co Galway, tall gravestones standing like barnacled old 18th-century veterans on a hump by the road. Here Blind Raftery, the 19th-century troubadour, is buried. His work is one of the rare sweet memories I have of being taught Irish, administered like a violent emetic by the Christian brothers.

He was a kind of Bobby Burns poet, fiddler, drinker, womaniser and curser of English authority. "Look at me now," he wrote at the end. "Full of hope and love/with eyes without light/Singing songs to empty pockets."

Then on down south towards Cork, reluctantly bypassing Farrahy, Co Cork (Elizabeth Bowen); we even gave William Trevor (Skibbereen) the slip because we were heading for a favourite literary semi-mythical town: Castletownshend. Not only was this the home of Edith Somerville and "Ross" (Violet Martin), two "refined", ie lesbian, early 20th-century authors, it is a town that is daftly moored in the old Ascendancy days.

A few years ago, the vicar, garage man, publican (can't remember if he was actually the boss or a semi-permanent customer), every conceivable profession, was in the hands of Townshends/Somervilles. The lady of the manor is still a Townshend. Rather bafflingly, the majority of this archetypal Anglo-Irish family all voted Fianna Fail. (De Valera had offered a protecting hand to them during the war of independence and they never forgot it.) The locals were always on the most amiable terms with their masters. It was here that Somerville and Ross produced their politically incorrect tales of the Oirish, Some Experiences Of An Irish RM. Somerville, who lived until 1949, continued to write under the same name for years after her partner died in 1915.

There is a point of sensory overload in these literary tours. When I got to Cork, I looked at what was to come - a menu of 16 more writers in Dublin. I caught the next plane back.

Way to go

Getting there: Easyjet (0870 6000000, easyjet.com) flies Luton-Belfast from £40 return.
Where to stay: McCausland Hotel, 34 Victoria St, Belfast (028- 9022 0200, mccauslandhotel.com), double rooms from £80 per night. Laurel Villa guest house, 60 Church St, Magherafelt, Co Derry (028-7963 2238, laurel-villa.com), £25pp B&B (two sharing). The Central Hotel, Donegal (00 353 73 21027), double room B&B €127. The Harbour Hotel, Galway (00 353 91 569 466), €99pp B&B. The Clarion Hotel, Cork (00 353 21 427 5858), double room, B&B€140.
Further information: The Literary Ireland map is published by the Irish Tourist Board (bordfailte.ie). Tourism Ireland information line: 0800 0397000, irelandholidays.co.uk.