Gareth Thomas thought he had seen it all when he joined Toulouse in 2004. He was then one of Wales' senior internationals, about to be made captain, and had enjoyed a high-profile career with Bridgend, Cardiff and the Celtic Warriors, a regional side which lasted one season before being closed down by the Welsh Rugby Union.

Thomas, who is now 34, spent three ­seasons with the French giants. Tomorrow afternoon he will face his former club for the Cardiff Blues in the quarter-finals of the Heineken Cup at the Millennium Stadium. Thomas played in the opening match at the ground, for Wales against South Africa, 10 years ago, and he appreciates that his next visit could be his last.

"Toulouse opened my eyes as a player and as a person," said Thomas, who in 2007 became the first Wales player to win 100 caps. "I returned to Wales 10 times better for the experience. I admit that when I went there I was not life-savvy: I was a wild child who lived life instinctively. I would walk past a building and not even notice it.

"In Toulouse, you immersed yourself in the culture of the place. The rugby team is a massive part of the city and generates a real passion but there is also far more to Toulouse. I learned not only to respect the history of the club but also the area and I soon came to appreciate ­buildings and structures. It freed up my mind completely and my time there was a life-changing experience, making me realise how fortunate I was.

"Before I went there, I took rugby and being a professional for granted. Wales was a goldfish bowl and I guess that, in its way, Toulouse was as well, except you felt you were in the sea. Everything that went on around you was on a bigger scale: the team became like a family to me and they were an amazing bunch of people."

Thomas had won a host of caps when he arrived in Toulouse. He made his Wales debut in the 1995 World Cup, when the game was still, nominally, amateur, but he was rarely a fixture in the side, flitting from centre to wing and having a stint at full-back. He gained a reputation as a physical three-quarter, not a reactive one.

"Toulouse expanded my game," he said. "You were given a freedom to play and express yourself on the field. Toulouse is the biggest club in Europe, rugby's equivalent of Real Madrid. Their game has always been about offloading and running but it is also physical, the complete ­package. It was always exciting, no matter how close a game was. I will always remember that constant feeling of excitement."

Thomas won the Heineken Cup with Toulouse in 2005. He will be among the Blues replacements tomorrow, having recovered from injury and illness, and if a feature of the French club over the years has been the quality of its bench (Yannick Nyanga, David Skrela and Clément Poitrenaud are among its occupants tomorrow afternoon), the Blues have developed a comparable strength in depth and six of their substitutes, including the Wales No8 Andy ­Powell, are internationals.

"I am delighted we are playing ­Toulouse rather than, like the Ospreys, Munster," said Thomas. "The beauty of the Heineken Cup is meeting teams from a different league. I am just delighted to be involved and the important thing for the boys is not to be overawed. We have to be bold and believe in ourselves. They are good, but so are we and we are playing in our own backyard. At this stage of my career, you appreciate an occasion like this all the more because you know it could be your last."

Thomas won his 100th and final cap in a calamitous defeat by Fiji in the 2007 World Cup. He led Wales then and always said he would never retire from international rugby. When Warren Gatland took over the national side at the beginning of last year, he left Thomas out of the squad and the Kiwi has never called on the player who led the Lions in the final two Tests of the 2005 tour to New Zealand.

"If I had gone on playing for Wales, I would not have lasted more than three or four games because of the physicality they have developed," said Thomas. "I would not be here now and how I appreciate just what a Heineken Cup quarter-final means. Not that long ago it would have been just another game of rugby, but I have been ­relishing this match ever since we qualified. [It is] a return to rugby's shrine."