SYDNEY, AUSTRALIA - JULY 08: A group of American nuns descend on Hyde Park ahead of World Youth Day Sydney 2008 on July 8, 2008 in Sydney, Australia. Organised every two to three years by the Catholic Church, World Youth Day (WYD) is an invitation from the Pope to the youth of the world to celebrate their faith. The celebration will be held in Sydney from July 15 to 20, 2008, and will mark the first visit of His Holiness Pope Benedict XVI to Australia.