Wales v Australia
Gregan has fond memories of playing in the Millennium Stadium
Millennium Stadium, Cardiff
Saturday, 15 September
Kick-off: 1400 BST
Live coverage on BBC Radio 5live, Radio Wales, Radio Cymru & the BBC Sport website
Scrum-half George Gregan says that Saturday's Pool B clash with Wales at the Millennium Stadium is a World Cup test that Australia are eager to take.
The Wallabies crushed a weakened Japan 91-3 in their opener, while Wales came from behind to beat Canada 42-17.
"A good tough game is a good measure of where you are as a group," said the most capped international of all time.
"And there's no better challenge than playing Wales in Cardiff, second match in a World Cup."
Gregan has fond memories of Cardiff, with his long time half-back partner Stephen Larkham helping Australia capture their second World Cup title in 1999 in the Welsh capital.
History shows that no team has ever lost a game and gone on to win the World Cup
Australia coach John Connolly
In that campaign, the Wallabies had to get past hosts Wales in the quarter-finals, beat South Africa in the semis and return to Cardiff to beat France in the final.
But at the Millennium Stadium in recent matches Wales have just held the upper hand, beating Australia in 2005 and then holding the tourists to a 29-29 draw last year.
Despite the ups and downs, Gregan still rates Cardiff as one of his favourite cities to play rugby.
The 34-year-old is looking forward to almost certainly his last Test match there, winning his 136th cap, before he ends his glittering career.
"I was fortunate enough to have played in the original Cardiff Arms Park in 1996 - I think I gifted Gareth Thomas an intercept try that day!" Gregan told BBC Sport Wales.
"Then obviously we had a wonderful time in 1999 during the World Cup.
"In recent years we haven't had such a great time here, but it's always a great place, a wonderful atmosphere, and the Welsh people are always very respectful of the game and the team that plays Wales.
"I love those sort of environments, it's a great spectacle and you're part of it.
"Lots of the guys who are in our 22 for Saturday are really looking forward to it, they've played in front of this Welsh crowd but never in such an important event."
Wales played two Tests down under as part of their warm-up campaign for the World Cup, losing to a last-gasp Stephen Hoiles try at the end of May in Sydney and then being well beaten a week later in Brisbane.
But Australia coach John Connolly said the results between the sides over the past two years would have little bearing on Saturday's game.
"This is a crucial game as far as our Pool is concerned and a lot of what we have done over the past 12 months has been preparing us for this game," Connolly said.
"I think we're a fair bit of the way down the road (from the loss and draw in Cardiff) and our form in the Tri-Nations showed that.
"History shows that no team has ever lost a game and gone on to win the World Cup.
"It's about building momentum and building confidence in the team and it's important in that respect."