Through the cafe window, Donnybrook Main Street is at ease in its mid-afternoon lull. Gordon D’Arcy is trying to get you to imagine the scene if there were people living on the side of the road — say three or four thousand of them between the rugby ground and Leeson Street Bridge. And they were up to their knees in filthy rainwater thickened by human waste.

Ostensibly, we’re here to talk about the imminent arrival of the Springboks, the team that knocked D’Arcy off his perch in Bloemfontein three summers ago. But he’s far more animated on the subject of seven deeply affecting days he spent working for Goal in Calcutta in July.

It’s five years since his first connection with the Irish-based charity — some small jersey-signing affair that prompted the idea of doing something more one day. Goal’s chief executive, John O’Shea, told D’Arcy he’d get him out to India some day after he’d retired from rugby. But D’Arcy rang earlier this year and told O’Shea he didn’t want to wait. He had no idea of what awaited him.

“Calcutta is the same size as Dublin but there are 14 and a half million people living there,” he says. “I was there in monsoon season. You’re talking two feet of rain falling in an hour or two. The sewer system is not designed for 14 and a half million people, so when it floods the whole city floods. There’s human faeces floating down the road and there are kids dipping tin cups into the gutter and pouring this over their heads to wash themselves.

“We met kids in the slums, myself and Paul Byrom, one of the Three Irish Tenors. I was lucky to be there with Paul because his singing helped break down barriers. He’d sing for them and they’d be in awe.

“A lot of the little girls had been abused, by fathers and brothers. They’d shave their heads to look like boys. So when they see a stranger for the first time, they’d be very wary of you. Once they see you’re not going to hurt them, they throw themselves at you. When Paul was singing sometimes, you’d have three kids sitting on your knee, four kids holding a finger. Then they all wanted to be in a photo. The affection they show you, it touches you very deeply.”

Days were long, up at 8am, working usually until nine at night. One day, they travelled three hours down deteriorating roads, then another three hours down the Bengali river to visit a hospital being built in Sunderbands. On the way, he saw children walking on six-mile journeys to school. A hunger for education was one of the most striking characteristics of the people he met.

“That’s the thing about India,” he says. “You have this thirst for knowledge and yet this awful lack of knowledge. We went to a farm where they were over-farming the soil because they didn’t understand the possibilities of crop rotation. As John says, it’s about breaking cycles of bad information.

“At no stage was I ever asked for money. They don’t want handouts, they want to be able to help themselves. They’re such a proud, proud people and they know that education is the way to a better life.” He says he feels privileged to have done this, to have been taken out of the bubble in which top professional sportsmen exist. Has it changed him? He already saw himself as being “a quite save-the-whale, tree-huggy kinda person” who tried to do right by others and he hopes that instinct has been strengthened by the experience. He is not the one to say whether he’s changed.

Several people have remarked on the apparent contradiction in his choice of motor transport. The BMW X6 doesn’t fit with the bandanas he occasionally wears, or the ear-stud, or the 1970s PLO scarf. Except that the gas-guzzling 4WD is not his choice but an endorsement deal, a perk that goes with the profile. Besides, he has a theory.

“I cycle to training four days a week,” he says. “It’s partly because it takes me 10 minutes to cycle whereas it would take me 35 minutes by car. But I would always walk or cycle if I was going into town.

“The other thing is I’m blessed with what I do and the situation I’m in. I won the lottery with the family I was born into. I’ve also been given a lot of opportunities and it would be very ungrateful of me not to take full advantage of them. Obviously, being a well-known sports person, this sort of stuff does come along. I’ve a great arrangement with BMW but one day it will all be over.

“Why would I not take it? The money I save on a car can be spent sponsoring a kid in Ethiopia or whatever. Why not make hay while the sun shines?”

HE’S on the bright side of the street right now. This must be the fifth interview we’ve done over the years and he has never seemed in better mental or indeed physical shape. He has always been helpful, enthusiastic and lively in conversation. Now, as he heads towards his 27th birthday, there is a certain serenity, too.

Already, he has managed to emerge from two significant troughs and has learnt to enjoy the good times when they come. He describes his first, well-documented, dip in succinct terms: “Got capped in the World Cup aged 19. Spent the next six months thinking I was better than everybody else, walking along with my head up my own ass.”

The second fall was from an even greater height but was all to do with injuries. In April of 2004, he was voted Player of the Six Nations, and by some distance. Two months later, he had the opportunity to show the southern hemisphere what all the fuss was about but the Springboks were waiting for him. He lasted just half an hour of the first Test in Bloemfontein.

“I got tackled late,” he recalls. “I’d passed the ball to Geordy (Geordan Murphy) but with the blitz defence the South Africans use, even if you’ve passed the ball (they’ll still take you with them). That’s the way they play the game, hard and physical.

“I’m not sure who it was but anyway, the ball is gone and I’m looking to run in support and he just grabbed my jersey and ran behind me. I did the splits in mid-air. I felt the pop. I even heard it.” He was back playing before Christmas but the groin problem was a complicated injury and hamstring problems came with it. He tore his hamstring twice during the Six Nations that season, once in Rome, once on the eve of the home match against England. He remembers “bawling, crying” in the snow up in Terenure College, with Eddie O’Sullivan trying to provide comforting words.

It was a year and a half before he recovered fully from that jersey-pull in Bloemfontein. He’d squeezed into the Lions squad, based on Clive Woodward’s memory of the carnage D’Arcy wreaked in Twickenham in 2004. But he wasn’t right, mentally or physically. By the time the Lions went home, the Kiwi media listed him in the “Five Lions Who Never Turned Up” category.

“The way I look back on it, Clive gave me every opportunity to perform, from the pre-tour test against Argentina right up to the Maori game. And I just didn’t perform. Some guys can explode back from injury. I didn’t, and I can live with that.

“One of the guys I got on very well with was Will Greenwood. I found him very energetic and entertaining. I actually learnt a lot from him. We both agreed we shouldn’t have been there. If this was a squad picked on form, we were two of about eight guys who shouldn’t have been there. I had no form whatsoever going into it. I was a ‘what if?’ selection. If the Lions tour was the summer just gone, I’d be much happier. I think I showed I wasn’t that guy who was there the previous summer.” The Kiwis, to be fair to them, appreciate grit and technical excellence under pressure, and that’s exactly what D’Arcy produced back in June, particularly in the second Test, played in wretched conditions at Eden Park.

He has carried that form into this season. He is in supreme physical nick. For D’Arcy, this means weighing in at around 88kg, which is roughly 14st, carried on a 5ft 10in frame (though he admits he puts down 5ft 11in when he’s filling in the forms).

In the 1970s, this would have been pretty respectable for an international centre; these days, it makes him one of the smallest No 12s around, especially now that the Wallabies have moved Matt Giteau to scrum-half.

Running at D’Arcy on Saturday will be Jean de Villiers, who is 6ft 3in and more than 15st. But D’Arcy’s used to it. Yannick Jauzion is even bigger than De Villiers, so too Rob Dewey, of Edinburgh, and others.

He survives in the heavy traffic because of his darting feet and his phenomenal core strength. Meanwhile, none of the bigger men possess what he can offer at the breakdown, where his poaching is matched only by Brian O’Driscoll.

England backs coach Brian Ashton said recently that the role of the No 12 was developing. With so much pressure now on the fly-half, the inside centre has to be a navigator as well as a carrier, a kicker and a distributor. The Wallabies, meanwhile, are trying out Stephen Larkham, who has played most of his rugby at No 10, for the role. D’Arcy, now in his third year in the pivotal position, is keeping an eye on trends but sees no need for radical change.

“I think the dynamic between Brian and myself works well,” he says. “We take pressure off each other. Rog (Ronan O’Gara) is good at seeing space so if I’m being lined up he gives Drico the ball and vice versa. We also have the ability to keep people guessing by switching positions.

“I’ve a big year ahead of me. I’m trying to learn as much as possible off Felipe (Contepomi) and Rog, trying to learn this role as ‘the new 12’. But I don’t want to change my game too much, either. Eddie’s great for me and for my confidence. He just wants me to do what I do naturally. There’s nothing better for a player than when the coach just says to you, ‘Do what you do.’ ”

O’Sullivan was pretty popular with his players on Friday. That morning, he told them training was cancelled — the week had gone so well, they could have the entire day off. According to D’Arcy, there was an upbeat atmosphere in camp all week, which helped to ease the pain of Leinster’s excruciating defeat at Murrayfield seven days ago.

“The Irish camp has evolved,” he says. “It’s something to do with the change of scenery up in Killiney, even a bit of change of personnel, some new faces. There’s something there and it seems to be working. Eddie’s going with the ebb and flow. Guys enjoy camp now. It’s just about keeping it going now.

“It might be something to do with the rivalry between Munster and Leinster — if you think about it, the last three games between us have been absolute belters. One thing I love about Munster is they expect to win and it’s the one thing Brian has been hammering into us as Leinster players.

“It’s coming with Ireland. I felt we earned last year’s Triple Crown a lot more than two years ago. People had written us off by last Christmas but we managed to sneak things around for the Six Nations. Then in June, I thought we did enough to win at least one of the Tests in New Zealand. From a poor start to the season, I thought we finished strong.”

Last season has wheeled into this one, and a few months down the line the World Cup will loom. It’s non-stop, but D’Arcy has already given time to think further ahead, to what happens when it all finally ends. He has four more exams to do this academic year to complete a degree in quantity surveying from DIT. Then he’s looking at project management.

“I’d like to do something that’s practically useful for Goal, when my rugby usefulness is over,” he says. May his rugby usefulness continue for as long as possible.