Speaking at the launch of Munster's new adidas kit, the Corkman gave a brilliant if perhaps overly descriptive insight into the Irish players' trips to the Polish town of Spala. Starting with the infamous chambers themselves.
"You're given an oul pair of socks, pair of boxers, a head band and mouth mask. It's minus 140 (degrees). You are in there for three minutes. They tell us if you did eight minutes you would die," explained O'Callaghan.
Sensing a chance to poke fun at his team-mates, he added: "If you are in there with Quinny (Alan Quinlan) you'll end up singing 'It's A Long Way To Tipperary.'
"There are a few games you can play to keep your mind off it. It's grand for the first minute of so...then the back of your knees start hurting. It depends on the fellas you are in there with really.
"If you are in there with (John) Hayes it can be incredibly smelly. (Peter) Stringer? It can be incredibly roomy and enjoyable. You've got to be very selective who you go into cryotherapy with. It's best off sticking with (Denis) Leamy as he just wants to get in and out."
As well as being physically demanding, Ireland's now notorious visits to Spala are tough on the mind also.
"There's nothing else (to do in Spala). It's really mentally tough," admitted O'Callaghan.
"You're there for five days. You have to clue in. You're there for nothing else but conditioning. It's quite tough. Everyone goes through their moments of breaking point. You're just hoping to get him perfectly at that time, around a group of lads, and hammer him.
"But you definitely feel the benefits, you couldn't get through the workload without it. There's some days you question why you're doing it but it stands to you at the end of big games - it gives you the strength to lift it and pull away."
Nearly five years a senior international, O'Callaghan is well-placed to judge the current mood of the Ireland squad pre-World Cup. And the 28-year-old has been encouraged by the improved bond within the current set-up, where provincial allegiances that perhaps created cliques in the past are now put to one side.
"You got to remember we are living out of a gear bag. Living with guys for seven, eight weeks. We know at the moment when guys need their space and when you can have a bit of craic. The maturity of the squad now means we respect each other a bit more," he said.
"I think it's maybe that we came through together. I played Under-21s with Drico (Brian O'Driscoll) and (Shane) Horgan. Neil Best and Rory Best are good friends whereas before you might have had more of a provincial camp.
"I'm not saying we weren't before but as a group we are real tight at the moment. I think that comes from going through the disappointments of the autumn internationals two years when everyone was on our back."