Twenty years ago, Sharabhang Giri was a Melbourne-based scientist who reluctantly went to India for a holiday.

Key points: A former Australian scientist is now a revered Hindu holy man in India

A former Australian scientist is now a revered Hindu holy man in India He's one of millions of believers who took part in the Kumbh Mela festival

He's one of millions of believers who took part in the Kumbh Mela festival The festival is the largest religious gathering on Earth and can be seen from space

When he arrived, he was an atheist with no real interest in the country.

"Someone brought me to India almost against my will. I had no plan, I got here completely by accident," he recalls.

Today, he's a revered Hindu holy man who says he can't even remember his name from his previous life.

"I found answers to all kinds of things that I'd been thinking about for a long time," he says of his conversion to the Hindu faith.

Foreign holy men — called sadhus — are extremely rare in India, so Giri attracts a lot of attention.

Especially at the Kumbh Mela — a gigantic gathering of the faithful that happens every four years at the confluence of India's most sacred waterways.

The Kumbh is the largest religious gathering on Earth.

150 million people visit the festival over two months and the sheer mass of humanity is visible from space.

The festival is so large that it is visible from space. ( AP: Rajesh Kumar Singh )

For a man who went to India on a whim with a friend, Giri looks very much at ease in the garb of a Hindu holy man; simple robes, long hair tied in a topknot and a flowing beard.

He still has a broad Australian accent, but rarely goes back to his homeland.

His mother is his only living relative, and when he visits her, he stays in an austere hut in Melbourne.

He spends his days roaming around India, visiting other holy men and gurus and living off donations from the faithful.

Giri's order is known for smoking cannabis to feel closer to their god. ( ABC News )

For centuries, sadhus have renounced the pleasures and possessions of normal life in order to pursue their connection with god.

Some orders of holy men eschew clothing altogether.

Others cover their bodies in cremation ashes, grow their hair into dreadlocks that touch the floor, or spend their days smoking copious amounts of cannabis.

Some sadhus go naked to feel more connected to their god. ( ABC News )

Holy men fear sacred festival is going commercial

Modernisation is putting pressure on the sadhus to change their ways, even at Hinduism's holiest festival.

Giri says the festival has become too reliant on technology. ( ABC News )

"There's much more technology involved," Giri says.

"There used to be a rule that you could only use canvas and bamboo [to build structures at the Kumbh Mela]."

But in 2019, simplicity has given way to modernity.

There are luxury tents for pilgrims who can afford them, although millions of worshippers come by train and sleep out in the open.

There are also giant posters of Indian Prime Minister Narendra Modi throughout the festival grounds.

Some people have complained that government has politicised the festival. ( ABC News )

His Government poured millions of dollars into infrastructure for this year's festival.

They've built new roads, bridges and lighting in a bid to consolidate the support of his Hindu nationalist base ahead of elections in a couple of months.

Even the name of the city hosting the Kumbh was changed by the Government last year.

The Muslim-sounding Allahabad was replaced with the Hindu-origin name, Prayagraj.

Some people have complained that the festival has become politicised, but many Hindus don't mind the Government spending money on religion.

Festival culminates in holy dip

The festival culminates with bathing in the holy water. ( ABC News )

For the sadhus and gurus, the highlight remains the bathing rituals at the centre of the event.

Giri belongs to one of the biggest monastic orders, or "akharas", in India.

Along with the most religious sadhus, on the most auspicious days of the festival he gets to bathe first in the holy waters where the sacred Ganges and Yamuna rivers meet.

Millions of everyday worshippers take a dip after the sadhus have had theirs.

"I'm not sure how many past sins have been washed away by the bath," he says.

"Hopefully I'll get into heaven. That's the point. Getting into heaven and not coming back."