By Christopher Landau
BBC religious affairs correspondent, Melbourne
This is only the fifth global inter-faith gathering to take place
What happens when an imam, a priest and a rabbi get into a lift together?
It may sound like a joke, but it is an everyday occurrence at the world's largest inter-faith gathering - and such unexpected encounters are positively encouraged.
The Parliament of the World's Religions has brought together representatives from 80 nationalities and more than 220 faith traditions for seven days of debate and dialogue.
The organisers hope that chance meetings in lifts, along with attendance at the 600 different formal meetings, will lead to new partnerships between religious groups.
This is only the fifth such "parliament" to take place.
A groundbreaking meeting between religious leaders from different parts of the world happened in Chicago in 1893.
One hundred years later, a group of inter-faith practitioners decided to hold another such meeting, and they have happened almost every five years since then.
The emphasis is on building relationships and giving members of each faith the opportunity to better understand several others.
There are no formal debates or votes, but organisers say that any commitments made by members of a particular community are formally recorded.
This parliament is distinctive because of the central role being given to representatives of Australia's aboriginal peoples - and to leaders of indigenous peoples from around the world.
Ten percent of the parliament's sessions are devoted to issues of concern for aboriginal and indigenous communities.
The opening ceremony began with a traditional aboriginal dancer accompanied by the didgeridoo, before an elder from the Wurundjeri people of Melbourne gave a formal welcome.
The parliament has given a central role to indigenous peoples
"We are grateful. We are honoured. We are privileged to have you here," said Aunty Joy Murphy-Wandin, before welcoming visitors with a traditional ceremony, symbolically inviting participants to share a leaf from "the branches of learning".
"I take a leaf in hope that you will accept this welcome to country," she said.
The opening ceremony also included performances from Melbourne's philharmonic choir and orchestra, plus formal blessings from the world's eleven major faiths.
A key area of debate and dialogue has been around environmental issues.
Indigenous leaders from northern Canada have highlighted how the effects of climate changes are already being felt in their communities.
Rev Dirk Ficca, director of the parliament, says that delegates are appealing to climate negotiators at the UN summit in Copenhagen to ask this question of themselves:
"Is the earth sacred enough to make those hard, courageous short-term decisions that will have implications for decades to come?
"Religious leaders are trying to draw on their wisdom and persuasiveness to make sure that we all believe it is sacred enough."
Concerns have been also raised about whether religious perspectives are taken seriously, particularly by secular governments in the West.
Prominent American rabbi David Saperstein told delegates that religious leaders must work hard to make their voice heard, particularly concerning the moral questions facing the world.
"We are the first generation that produces enough food to feed every human being on earth. Our failure to do so now is a failure of moral vision and political will.
"In a world in which you can do everything, what you should do - the moral question - is the fundamental challenge facing humanity. And on that question, the religious communities have urgent, profound, indispensible wisdom to offer" he said.
The parliament could hardly be accused of failing to account for the broadest possible range of spirituality and religious experience.
Pagans, Zoroastrians, and even atheists make up the rich mix of perspectives.
Organisers have faced some criticism for giving a platform to the Church of Scientology - which some accuse of being more of a business than a conventional religion.
Aunty Joy Murphy-Wandin invited participants to share a leaf from "the branches of learning"
But this is an event which is prepared to given even the most unusual new religious movements a fair hearing.
The parliament's marketplace offers a glimpse into some of the more unusual spiritual experiences on offer - often only for those prepared to pay.
Leaflets for new initiatives might also raise a few eyebrows. Plans to turn the island of Alcatraz into "a jewel of light" promise "a new, peaceful and enlightened epoch for all humanity".
Meanwhile the "Skywheel" sacred art project hopes to send a satellite into space with thousands of copies of prayers wound inside a prayer wheel, "radiating its blessings to the universe above and our world below".
But however eccentric some of the fringe offerings, the parliament also attracts a wide variety of prominent, mainstream leaders.
From the Dalai Lama and a senior Catholic Cardinal to young community activists, there seems to be a space for anyone of faith who is prepared to engage with others in a spirit of goodwill.
There have been some tense exchanges. The religious freedom in Iran of members of the Baha'i faith was raised with an Iranian speaker; the Roman Catholic church was challenged on its opposition to using condoms to halt the spread of HIV/Aids.
But most of the time this event achieves what so often seems a distant hope in today's world: honest, genuine engagement between people from very different backgrounds, holding profoundly different beliefs.
It may be limited in clear, concrete results, but the parliament certainly helps build relationships across religious traditions - and that alone may offer some hope for fewer religious divisions in future.