There is really only one mysterious rail journey left for the sensitive and thrill-seeking traveller in Europe. If you want to experience the two Irelands in safety and comfort, and without having to tramp through dreary back streets, the journey for you is on board The Enterprise.
Stroll out of the Georgian magnificence of Trinity College, Dublin, pausing for a good pot of tea ("leaf or tea bag, sir?") and a coffee eclair at Bewley's Oriental Cafe. Cross the quiet Liffey by O'Connell Bridge, skirt the wonderful 18th-century Customs House and wander up Amiens Street to Connolly Station.
At 1.20pm, for a return fare of pounds 26, you can take the new French-built train, a gleaming 21st-century monster worthy of competition with Eurostar, to Belfast - and contemplate the two worlds of Ireland.
The departure announcement is made, doors hiss shut on our carriage, my Colombian friend Alfredo and I settle into our comfortable seats and glide past the people on the homely-looking train due to leave five minutes later for Maynooth, Mullingar, Carrick-on-Shannon and Sligo.
In a silent comfort the Orient Express could not offer, and with the exotic touch of notices in English, Irish and French, we pick up speed through the suburbs of north Dublin. The seaside villages of Malahide and Balbriggan flash past, the rusting carcass of a wrecked vessel here, smart new seaside flats there. Over the river Boyne we fly across the great viaduct at Drogheda, the town whose inhabitants Oliver Cromwell massacred in 1649. Below are the waters that will always recall Protestant King Billy's victory over the Catholics in 1690.
On to Dundalk, the last town in the republic before the border, a place where republicans sought by the Royal Ulster Constabulary take refuge, there to be observed minutely by the Garda Sochna, the Irish police. The border between the Republic and the United Kingdom of Great Britain and Northern Ireland is crossed with not so much as a touch on the brakes - but all except the least alert traveller will notice an immediate difference, and not just because the ground rises as we push on towards the Mountains of Mourne.
This is South Armagh, a particularly republican part of the world. Fortresses top the hills and they are not of the charming, ruined, medieval sort that you see in Yorkshire, Wales and Scotland, garrisoned by middle-aged ladies from the National Trust. These are modern electronic edifices with machines capable, they say, of telling their army garrisons how many times Mrs O'Grady flushes her toilet or what Pat and Mike are talking about as they cruise by in their Ford Fiesta.
Perhaps they are listening now to what we passengers are saying on the 1.20pm.
The train rounds the side of a hill above Newry, where Irish tricolours sprout from telegraph poles to signify that some of Her Majesty's subjects are Hers unwillingly. Downhill from Newry station is a tidy UK roundabout with the neat lettering and road numbers in the typeface prescribed by the Department of Transport in London.
It takes precisely 20 minutes to get from Catholic, republican Newry to Portadown, the citadel of Protestant Unionism. As though not wanting to recall the scene, we whizz through the deserted station at Pointzpass, the scene last year of a spectacular sectarian murder of two friends, one Catholic, the other Protestant.
It's 40 minutes on to our destination - no time for a stop at Lisburn, seat of the British military high command in Northern Ireland. Before long the pleasanter suburbs of Belfast come into view. Botanic, the station that is the gate to the smart pubs and restaurants of Belfast's dolce vita, goes by as the driver starts to slow down. Three minutes before the scheduled arrival of 3.30pm, we pull into Belfast Central.
Just beyond the fence, another Irish tricolour flies from a telegraph pole, signifying the existence of a little, isolated pocket of Catholics proclaiming their loyalties amid an overwhelmingly Protestant area of the Northern Irish capital. There is one last ritual.
As we walk up the ramp to the station exit, men in uniform with dogs appear. "Keep over to the right, please. Single file, single file now." Obediently we do as we are told as I recall Checkpoint Charlie in the Berlin of the Sixties.
I explain the situation to Alfredo, and our Spanish alerts the forces of law and order trained to the highest levels of alertness. Had the animals been trained to sniff for drugs or for dangerous republicans seeking the overthrow of Her Majesty's Government in Northern Ireland? I didn't know, but Harry Lime would have. He would have been a useful companion on the most politically charged train ride in Europe.
YOU CAN, of course, start at either end of the run. There are plenty of cheap flights to both Dublin and Belfast from various points in the UK - notably on Ryanair (0541 569569) to Dublin, and easyJet (0990 292929) from Luton to Belfast. Other airlines with scheduled services from Britain include Aer Lingus (0645 737747), British Airways (0345 222111) and British Midland (0345 554554).
Perhaps the best bargain to Dublin, for passengers wanting a largely unrestricted ticket, is on Virgin Trains (0345 222333) and Stena Line via Holyhead and Dun Laoghaire. Travellers from London pay pounds 39 return.
Northern Ireland Railways enquiries: 01232 899411.