A modified Civil Service office block within the sprawling Stormont estate in east Belfast, it has been described as "the original sick building". It is cheerless, characterless and boxy. Because it suffers from a lack of natural light its corridors are particularly brightly lit, its stark Sixties design offering few intimate corners conducive to private politicking.
Gerry Adams once compared it to the RUC interrogation centres with which he became familiar in the 1970s, calling it "Castlereagh with coffee". Apart from anything else, party delegations can glance out of their windows to see a little waiting knot of television crews and reporters, a constant reminder that every move is under scrutiny.
The Mitchell review of the peace process was planned, every detail looked at with meticulous precision. Those involved knew it was seen as possibly the last best chance to break the deadlock which had drained both momentum and credibility from the process.
Among the details trawled over in advance by the two governments was the question of where the discussions should be held. Thus it was that the men of both sides of the Northern Irish divide were brought together at Winfield House, a venue which helped breathe new life into the delicate negotiations. The Stormont building was used too, but so were numerous secret locations provided by the Government, away from the media's prying gaze.
George Mitchell conducted every talks session himself, never taking officials into the room with him. He very rarely made notes during meetings, though afterwards he kept a careful record of the important points.
The general format was mapped out well in advance by the British and Irish governments in concert with Mr Mitchell, with both Mo Mowlam and the Irish Taoiseach Bertie Ahern intimately involved. The staff working behind the scenes were headed by two officials, Bill Jeffrey on the British side and Dermot Gallagher from Dublin. Jeffrey, a quiet but effective Scot, has been political director at the Northern Ireland Office since early last year. Gallagher, an old Anglo-Irish hand, was formerly Irish ambassador to Washington.
Peter Mandelson, the new Northern Ireland Secretary, was highly supportive. His arrival was welcomed by Unionists as a boost, partly because they disliked Dr Mowlam so much and partly because they suspected he might be more favourably disposed towards unionism.
One source said: "There was strain between the Unionists and Mo Mowlam. With Mandelson that's not there any more; there's been a definite relaxation." Mr Mandelson himself, aware of this, made a point of indicating to the Unionist leader David Trimble that his people would be ill advised to allow the Mitchell review to fail. It was made clear that Unionists should not expect to win significantly better terms if they marked time and awaited some subsequent initiative personally driven by the new Northern Ireland Secretary.
David Trimble, ever nervous about carrying his divided party with him, at first brought large delegations along, trooping in with teams of seven or more. But George Mitchell suggested that give-and-take would only realistically take place with much smaller numbers.
In the end Mr Mitchell got what he wanted: talks involving only two from each side. So the main discussions involved Trimble and east Belfast businessman Sir Reg Empey, while from the republican side came Gerry Adams and Martin McGuinness.
The early exchanges were, in Mr Mitchell's words, "harsh and filled with recrimination". One close observer said: "At the start it was almost like In the Psychiatrist's Chair, with people offloading their grievances about the summer and how they felt they'd been hurt by the other side. But then it moved on from that."
At Winfield House they not only worked together, but dined together. Mitchell insisted that they mingle at the table, not wanting to have all the Unionists sit on one side and all the nationalists on the other. This was new: republicans and Unionists have rarely socialised together.
He made another important stipulation, too, as he explained: "I insisted that there not be any discussion of issues at the meals, that we just talk about other things so that they could come to view each other not as adversaries but as human beings and as people living in the same place and the same society and wanting the same thing."
It worked. It was at Winfield House that Unionists and republicans were able to see the whites of each others' eyes and conclude that they could do business with each other.
The Government, anxious to provide as much privacy as possible, had a gap in the fence filled in to block the view of the television cameras. However, the two sides did not ignore the media: news filtered out from both, but in general it took the form not of destructive leaks but of soothing noises of reassurance to their respective grassroots.
Inside the talks there was a significant softening, one insider reporting: "The body language changed after Winfield. Before that it was always stiff and stilted, but afterwards they no longer seemed instinctively uncomfortable in each other's presence. Winfield was the psychological breakthrough."
But increasing familiarity played a large part too. Over the 10 weeks the two sides had close to 300 hours of face-to-face talks. This statistic is rendered all the more remarkable by the fact that Trimble and Adams spoke together for the first time only in September last year.
Their sporadic encounters since then have not been reckoned as great successes on either a social or a political level. Even at Winfield, in fact, Trimble is said to have struck up a better rapport with Martin McGuinness than with Adams. At a key point Mr Trimble reached a decision that he needed a variation on his party's familiar mantra of "no guns, no government", concluding that the IRA was simply not going to decommission weapons simultaneously with the formation of a new executive. He settled instead for the idea of statements from the IRA and Sinn Fein, reiterating the republican commitment to the peace process and confirming that the IRA would appoint a go-between to meet General John de Chastelain's disarmament commission.
Though this fell well short of a formal guarantee of IRA de-commissioning, the political calculation was that republicans will be condemned if they pocket the Unionist leader's concessions while simply stone-walling on the arms issue. This was something; the question was whether it would be enough to sell to his notoriously suspicious party.
There were some tense moments when Trimble returned to Stormont to brief his assembly members, some of whom refused to back him. And in the republican community the deal has been swallowed rather than welcomed. A number of senior members of Sinn Fein and of the IRA quit when they saw the unprecedentedly pacific rhetoric of the former and the action of the latter in appointing a go-between with General de Chastelain.
The worry of those who have left is the mirror image of what Mr Trimble hopes - that the republican movement has embarked on a path which will inexorably lead towards decommissioning, and to a reliance on political means alone.
The stream of statements from Unionists, republicans, Mr Mitchell, General de Chastelain and others since then has been agreed in advance and is being carefully co-ordinated. The Unionists and republicans have in fact agreed to run their statements past each other to help avoid destabilising rows.
This is unprecedented, as were the talks themselves. They represented the first time that republican and Unionist moved beyond challenging each other and got into the business of working out what was possible for the other side to deliver.
This has brought the peace process to the point where, if all goes well and Trimble wins his party's formal endorsement, a new cross-community government could be in being by Monday week.
Getting to this point has been a long and arduous business, and the process will undoubtedly be buffeted by recurring crises. If it eventually succeeds, however, there will be widespread praise for both Trimble and Adams, and widespread gratitude for American hospitality, in the form of Winfield House, and American political know-how, in the person of George Mitchell.
The decision of George Mitchell (above left) to hold his review away from the media spotlight helped to break down distrust between the Unionist and Sinn Fein delegations (above right) PETER MORRISON/AP, JOHN STILLWELL/PA, PAUL McERLANE/REUTERS