Sydney - Notoriously grumpy Sydney residents were Saturday beginning to discover what the people of Cologne found three years ago: hosting young Catholic pilgrims can be fun. 

Complaints about packed trains and traffic snarls gave way to wonderment at the happiness of the 125,000 foreigners in town to meet each other and perhaps get a close up view of Pope Benedict XVI. 

The switch from frowns to smiles will come as no surprise to Bishop Anthony Fisher, chief organizer of the World Youth Day celebrations that culminate with a papal mass July 20. 

"When they see the bunch of lovely, happy, idealistic young people, I think they'll be swept along with that - and I don't think we'll see any trouble-making," Bishop Fisher predicted. 

More than 150,000 pilgrims are expected to be on the foreshore to greet the pope when he makes a grand entrance on the harbour on Thursday. Up to 500,000 could be at the closing Sunday Mass that ends the pope's first visit to Australia. 

World Youth Day, begun in Rome in 1986, is held somewhere in the world every three years. Cities bid for it, just as they do for an Olympics. 

The trouble-making that Bishop Fisher fears is that promised by the NoToPope Coalition, an alliance between gays and lesbians angered by the church's teachings on sexuality and anarchists disturbed by new police powers rushed through to bolster security at an event costing the taxpayer over 100 million Australian dollars (94 million US dollars). 

The NoToPope Coalition intends handing out condoms to pilgrims and marching with anti-Catholic slogans at World Youth Day venues. 

Also out to rain on the papal parade are those championing the victims of sexual abuse by priests. Demonstrators outside Melbourne's St Patrick's Cathedral are calling on Pope Benedict to repeat in Australia the apology to victims he made during his April visit to the United States. Most likely he will. 

World Youth Day draws in the Catholic Church's big guns: the Holy Father and 80 Cardinals. But the key participants are young people from over 170 countries, many of whom have had to scrimp and save for years to get to Sydney. 

They come looking to revitalize their faith and make sense of religious observance in the modern world. 

"A lot of young people are looking around and seeing a world that is very fast and very materialistic and there is not a lot of time to contemplate spirituality," local pilgrim Alice Woolven said. "When you walk into the church, you leave the outside world behind. It's timeless." 

Also timeless is the joy of youth. 

German pilgrim Karl Von Furstenberg, in Sydney for his fourth World Youth Day, was over the moon about all the hymn singing, the dancing, the bible study and the companionship. He said it was "fantastic to be part of the living church." 

"It's fantastic to be here," he said. "We are Germans and we have to come to Australia because the pope is a German." 

The 81-year old pontiff arrives Sunday, but will keep out of the public eye until he boards his boat-a-cade and sweeps past the Opera House and under the Harbour Bridge for his first meeting with a congregation of up to 150,000 young people. (dpa)