Fear of being naked in public was just one of the challenges faced by many of participants, who flocked into the CBD from 4am today. Queuing was to be a hallmark of the day as people queued to get in, queued for the loos, queued for coffees, and, yes, even queued to strip off.

My friends and I left Neutral Bay just before 4am and, after a dream run into the city, came to a screeching halt at the corner of George and Bridge streets. Impatient as we were, it gave us a chance to check out the people in the street. Clearly, at this time in the morning, they were all heading to the same place we were. There were elderly couples walking down Macquarie Street, single young women in cars and plenty of gay groups whooping it up as they headed down towards the Quay.

After 45 minutes stuck in a traffic snarl of soon-to be naked people, we finally emerged from the Opera House car park. By the time we arrived, the 2500 tickets to a second photo shoot inside the Concert Hall had already been given away. We were each handed a plastic bag for our clothes and directed into a marshalling area inside The Domain.

Soon after we arrived, a loudspeaker crackled into life and we were instructed to keep our clothes on for the time being (not hard considering it was a nippy 15 degrees) and to await further instructions. About 6am, Tunick welcomed us, thanking the "heterosexual people who have come here to get naked with their gay friends". Just on dawn came the instruction that everyone had been waiting for. There was a whoop and a cheer from the crowd as the first group disrobed and ran into the forecourt.

Finally it was our turn and, in no time, we were running up the Opera House steps in a state that on any other day would get us arrested. One woman beside me shouted to her friend: "This is surreal. It's like a dream."

"It's like my worst nightmare," groaned her friend. The excitement was palpable, to be standing naked in such a public place and among so many people. But quite soon the cheers were replaced by "oooooh" as a chilly wind blew up.

Inhibitions were soon forgotten as people struggled to keep warm and fulfil Tunick's endless instructions. "I'm not the world's best photographer but I am an artist and a perfectionist," he said, as he exhorted 5000 people to work in unison.

"And I want us to make an artwork you'll be proud of." Six or seven positions later came Tunick's most confronting request. "If you came with a partner, I want you to kiss your partner. If you came with a friend, I want you to kiss your friend. If you came alone, I want you to turn to someone else who is alone and kiss them."

Eventually he relented and added "or embrace them". Suddenly I was aware of being alone in a crowd: I was surrounded by couples. Bounding up several steps I came face to face with an elderly man in the same predicament. We took one look at each other and embraced, admitting that, while it felt a little strange at first, it was a pleasant enough way to keep warm. Now the crowd really were as one. It was a beautiful moment.

Once Tunick gave the disband signal, most people scrambled for their clothes, while some hung back, grabbing the unique opportunity to take happy snaps of themselves starkers at the Opera House. As I dressed, I was relieved to be warm again at last but also a little disappointed that it was over so soon.