As a team of Irish doctors approached Bergen-Belsen, the Nazi concentration camp liberated 75 years ago this week, they became aware of "a disquieting aroma" that came to them in wafts, gradually filling the air in the truck around them.
"It was the Belsen smell of death and decay," paediatrician and former rugby international Dr Bob Collis later wrote in his autobiography, To Be a Pilgrim.
He went on to describe the unthinkable conditions: the British Army had discovered unburied bodies - 10-feet high in places - and thousands of starving people when it liberated "The Horror Camp", as it became known, in northern Germany on April 15, 1945.
When he saw emaciated adults and children in the most appalling conditions, dying at a rate of 1,000 a day from starvation and typhus, Dr Collis enlisted more help from the Netherlands.
Then, he set to work in Belsen with his fellow Irish doctors - surgeon Nigel Kinnear and paediatrician Patrick MacClancy - who had all volunteered with the British Red Cross.
Dr Collis was in charge of two blocks that housed a number of orphaned children. On his rounds one day, he recalled meeting the "most entrancing scrap of humanity" in the arms of Dutch volunteer Han Hogerzeil, who would later become his second wife.
He was describing a little boy called Zoltan Zinn, from Slovakia, whose smile seemed to be all there was of him - the rest of his body had been wasted by typhus, Dr Collis wrote.
Zoltan and his sister Edit, along with Hungarian siblings Suszi (Suzi) and Tibor (Terry) Molnar, became what Dr Collis described as "his special children".
When they went to Sweden to convalesce, he committed to taking them back to Ireland with any others who didn't have homes.
A year passed and when they had recuperated, Dr Collis made preparations to bring five children to Ireland and to care for them at Fairy Hill, an open-air hospital in Howth, Co Dublin.
He adopted Zoltan and Edit himself, raising them with support from his first wife, Phyllis, with whom he had two sons, Dermot and Robbie.
He arranged for the adoption of the others: Suzi and Terry were adopted by Elsie and Willie Samuels in Dublin, while Evelyn Schwartz went to Australia. She still lives there.
Looking back, Suzi Molnar (now Diamond) recalls the remarkable actions of a man who brought five children to Ireland and arranged for them to stay, even though they didn't have papers.
In recognition of his work, he was presented with a six-branched candelabrum, representing the six million Jews murdered in the Holocaust.
Suzi says the inscription sums him up perfectly. "It read 'Healing requires to be inspired by love' and to me that is him to a tee. He wasn't looking for profit, or for recognition in any way."
To do what he did, though, required self-belief and conviction.
As Suzi recalls, he believed he was right and used that belief in his practice of medicine.
For instance, when Zoltan fell ill with tuberculous meningitis in Ireland, Dr Collis used a new medicine, streptomycin, which he had received only days before.
Dr Collis resumed his medical work as head paediatrician at the National Children's Hospital in the same pioneering spirit, focusing as he had done before on the plight of people living in the overcrowded slums of Dublin. He was particularly worried about the child mortality rate and tuberculosis.
He also did ground-breaking work on cerebral palsy and helped to found Cerebral Palsy Ireland.
Christy Brown, who suffered from the condition, was a patient, and Dr Collis encouraged him to write My Left Foot.
Indeed, Brown recalled that his doctor initially dismissed an early draft as "awful" but, while reading it, suddenly slapped the table and said: "Good!"
Dr Collis went on to explain: "You have written one sentence here that stands out like a rose among a lot of weeds, one shining little gem thrown in amongst stones. It shows me that you could write if you knew how. That's what I wanted to find out."
Robert Collis, as he was known when he wrote, was a gifted writer himself and wrote two plays: Marrowbone Lane, about life in a Dublin slum, and The Barrel Organ.
He also wrote several books, including his autobiography, a book on Bergen-Belsen and two on his experiences of working as doctor in Nigeria in the Fifties and Sixties.
When his sons were older, he divorced his first wife, though they remained on friendly terms.
He married Han Hogerzeil and they had two sons, Sean and Niall.
The couple retired to the Wicklow Mountains in the Seventies, where their nephew, Uto Hogerzeil, still lives.
Uto remembers Bob Collis as a larger-than-life figure with deep passions. He came from a line of Anglo-Irish gentry and was sent to Rugby School in England; he later studied at Cambridge.
When he got married, his father gave him a house at 26 Fitzwilliam Square in Dublin as a wedding present, so that he could set up his surgery.
Despite his background, he had a social conscience and, with Han, wanted to help others.
Their nephew recalls: "They were never interested in enriching themselves. They were desperately trying to do good. They were unselfish in their outlook on life. They didn't even have a pension."
The other side of that was he tended to be more interested in the big picture rather than the small details of family life.
In his memoir, Final Witness, his adopted son Zoltan wrote: "He was like Francis Drake, or Walter Raleigh - an adventurer. Great on an open sea with the wind in his hair; less great in the small pond of family life."
His nephew describes a man who could be impatient, but who had a great sense of humour and was endearingly eccentric. He might wear odd socks, or have a hole in his jacket, or, say, if he was given a biscuit for the dog, he might eat it himself, Uto laughs.
Uto believes it is very important to mark the 75th anniversary of the liberation of Bergen-Belsen this week and to remember what his aunt Han and her husband, who died aged 75 in 1975, did to expose the horrors of the Nazi regime.
When Dr Collis left Bergen-Belsen in 1945, he described those degradations in a chilling passage: "On the day we burned down the Horror Camp with flame-throwers, a cloud of smoke and mist hung over the scene giving the spectacle of the jets of flying flames a diabolical appearance so that we felt the wickedness of that place existed as positive Evil, that in fact positive Evil really exists in the world and the old concept of the Devil may be true."
While it is hard to look back, it is vital we do so because, as Holocaust survivor Suzi Diamond says, history can repeat itself.
"Maybe not exactly in the same way, but we must be on our guard against bigotry, racism and anti-Semitism whenever they show their ugly heads."