If you have spent any time at the UN headquarters in New York, the building that houses UN agencies in Vienna is comfortingly familiar.
You recognise it from the moment it looms out of the Danube fog - a sweeping curve of high rise concrete, with splashes of startling orange to alleviate the grey.
The real drama has been in the back room gatherings, not the meeting itself
Once inside, the atrium foyer also follows the UN model - the same canopy of world flags fluttering overhead, and below the same well-worn exhibition on an improving global theme, being dutifully visited by Austrian schoolchildren.
And everywhere the cosmopolitan hum of UN workers, ostensibly busy as bees in a hive, but really, I always suspect, on a mission to beat the lunch queues in the subsidised canteen.
Add the eye-smarting, slightly rancid odour of cigarette smoke, the journalists staked outside a closed door with cameras and laptops at the ready, and you know this is the Vienna home of UN diplomats when history may be in the making.
And this last week there was certainly a sense of anticipation.
Leaders in Europe, and even US President George W Bush, insist that this time military action is not on the agenda. But the Iraq experience has made us wise to how far in advance diplomats plot their chess moves - every word and comma in a draft resolution may conceal a buried purpose, every obscure reference to an earlier document may be a seed, planted to justify some course of action later.
Iran has been desperate to stop the IAEA reporting them
No wonder the quibbles over seemingly innocuous phrases can go on for days.
Curiously, it was the Iranians, those most anxious to see any resolution fail, who most clearly signalled how important this week could be.
British and other European diplomats all insist it is not really that big a deal to report Iran to the UN Security Council. Nothing would happen for a month, they told us, and even then, all the Security Council would do was consider a series of graduated steps, probably starting with a mild request that Iran should be a bit more co-operative.
But the Iranians are jittery. On Wednesday the Iranian ambassador invited us to an hour-long power point presentation, to launch a desperate appeal.
"If we are reported to the Security Council, you will be making a serious historic mistake," he said. "Don't use the language of threats.
"The Iran government is sensitive and responds badly to threats. We are beginning to understand the bitter experience of Iraq."
But the real drama in Vienna has been the back room deals that provide a fascinating insight into where the world's current fault lines lie.
For British diplomats, for instance, the achievement thankfully is that this time we are not at odds with the French and Germans, uncomfortably exposed as George W Bush's poodle, even if relations with Iran have gone down the tube.
This row over Iran is as much about energy politics as the prospect of nuclear weapons
And when Europe is united, its clout, it turns out, is considerable - besides its own 25 members, in Vienna it enlisted the backing of pretty well every country that one day hopes to join the club, from the Balkans, to Turkey and Ukraine.
Very different from America's backyard, where Cuba is now joined by Venezuela in resolutely voting against what it sees as bullying by the US. And with them, Syria, another country that knows what it feels like to be the target of America's wrath.
And that leaves in the middle a broad swathe of countries, some from the Islamic world who do not want to gang up against a Muslim brother, others from non-aligned countries, reluctant to endorse America's lead, and others caught in an energy trap of reliance on imported oil.
Russia the lynchpin
Indeed, arguably this row over Iran is as much about energy politics as the prospect of nuclear weapons.
Those fast-growing Asian economies, China and India, for instance, are both reluctant to take any step that might jeopardise much needed oil supplies from Iran.
There's nothing Russia likes better than to have other countries, and especially the United States, acknowledge that it has a pivotal role to play
And India's dilemma has been even more acute - it has found itself caught between not wanting to upset Iran, and the need to keep on side with President Bush, who is due in Delhi next month with an offer, if all goes well, to help develop India's peaceful nuclear power.
But the lynchpin, it seems, is Russia, both oil-rich and Iran's closest nuclear partner. Whatever the outcome of this crisis, Russia stands to gain and lose - and this week, it seems, Russia has decided to come down off the fence and support the West's call to notch up the pressure on Tehran.
Why? Western diplomats say Russia too is worried about Iran's nuclear programme, and is working on a compromise plan. But perhaps above all, there's nothing Russia likes better than to have other countries, and especially the United States, acknowledge that it has a pivotal role to play.