For me, it is the suitcases. The ancient brown leather is battered and crumpled. But the letters are clear enough. Each bears only the name and date of birth of its owner. Some belonged to adults. But many belonged to children. It is not hard to imagine how the child's mother selected the bare essentials to pack – the Nazis often provided lists, reminding mothers not to forget their child's favourite toys – while their father lettered the outside of the case in white paint – to make sure that things went as right as they could for their little one.
Some of the lettering is clumsy, but on most cases it is careful – in cursive script, in block capitals, in neat italics. Each is individual. It is the kind of thing every parent has done when their child is going off on their own for the first time. Love as preparation. Sometimes that is all you can offer to accompany them. But these children were not going on a school trip. They were going to Auschwitz.
For Stephen Guy, it is the photographs of the countless inmates in their rough-cloth striped uniforms, which line the corridors of one of the prison blocks. Stephen is a lecturer in communication and culture at Stourbridge College, a further- education institute in the West Midlands. He pauses before the long row of images. "There is something about the process of starvation that is also a process of dehumanisation," he says. "The more people are starved, the more they look the same – the eyes protrude, the cheeks hollow, the faces become skeletal. Then their heads are shaved, and they all wear the same prison uniform. It drains their individuality, which must have made them easier to kill. But that girl there," he adds, pointing, "she looks like one of my girls at school."
For Manprit Gill, it is the story told by a colleague who visited Auschwitz the year before on one of several dozen trips organised for pupils and teachers by the Holocaust Educational Trust. "She was OK until she got home," Manprit, from Barr Beacon College in Walsall, where she teaches Good and Evil to Year 9, tells me. "Then she took one look at her own children and burst into tears. We all live with our own consequences," she says elliptically and lapses into silence.
A journey to Auschwitz affects everyone differently – though quite what is the impact of this louring place upon those who go there as part of a stag weekend is hard to imagine. Yes, there are stag weekends to Auschwitz now, or more specifically to the beautiful medieval city of nearby Krakow. They consist of a vodka-drinking competition on Friday evening, a night in Poland's "coolest club" on Saturday and a day of shooting pump-action shotguns and automatic rifles at a local gun club on Sunday. On the Saturday they slot in a bus ride to the death camp. With nigh-on 600,000 visitors a year, the Nazi concentration camp is now, bizarre as it might seem, one of Europe's leading tourist attractions.
But for those who today pass beneath the gateway to the first of the three Auschwitz camps – with its cruel lie of a wrought-iron motto "Arbeit Macht Frei" ("Work makes you free") – it is an experience which reduces most visitors to a stunned silence. Nothing you have read or seen quite prepares you for the cold and calculated reality.
First, you come to the kitchen block, where the inmate-workers were musicians whose surreal secondary task was to play Mozart to new arrivals – to delude them into a sense that the place could not be as bad as it was going to be. Then the brick-built blocks with tiers of shoddy wooden bunks, contrasted with the solid-marble water troughs in the washing-rooms, used by inmates before they left the camp each day to work in local factories.
Next comes the hospital block, where the camp doctor, Josef Mengele, and others did experiments without anaesthetic on thousands of twins, dwarfs and people with physical abnormalities. They tested out methods of quick sterilisation, some very painful, so that healthy Jews could be kept for slave labour but prevented from breeding and crowding the "living space" for the Aryan race.
And, finally, the prison block, where the Gestapo had their HQ with starvation cells, coffin-like oxygen-deprivation cells and chimney-like cells, barely a metre square, in which four or five prisoners would be forced to stand for days on end, for crimes as trivial as smoking or talking in working hours.
The cellar is still there in which a cyanide rat-poison gas called Zyklon B was first used on people to test whether it might be used for mass exterminations of undesirables. The head of the SS, the former chicken-farmer Heinrich Himmler, arrived at the camp in June 1940 to approve the gas. He then ordered construction of a far bigger site, Auschwitz II-Birkenau, which was to be not merely a work camp but a death camp in which the "final solution of the Jewish question" was to take place.
The first Auschwitz prompted a steady flow of bewildered questions from my party. But as we enter the gatehouse of Auschwitz II – through the archway under which so many had passed on a terrible one-way journey – silence falls like a seeping cloud on the group of teachers I have joined on this latest Holocaust Educational Trust visit.
Slowly we walk down the single track of railway line from the gatehouse and watch it divide into several sidings as it approaches the selection area, where a doctor would casually divide the disembarking crowd into three: men to the right; women to the left; children, the elderly, the handicapped, pregnant women, women with small babies – and any others deemed to be unfit for work – straight on.
It is a walk of perhaps 400 more yards. At its end, just before the grove of birch trees from which Birkenau took its name, stood four brick-built extermination buildings, each with a separate changing-room, gas chamber and crematorium. They are in ruins now. The Nazis blew them apart in 1944, as the Soviets approached, in a last-minute attempt to hide what was perhaps the most monstrous crime in human history. A mind-numbing 1.1 million people, 90 per cent of them Jews, were exterminated here. If you were to mark one minute's silence for every person who died, it would take you two full years.
Even in a century which contained mass murder in Armenia and in the partition of India, the Soviet gulags, the killing fields of Cambodia and attempts at genocide in Bosnia, Rwanda and Darfur, there is something peculiarly chilling about Auschwitz. Perhaps it is because this was not some alien machete-wielding bloodlust. It was methodical and systematic and conducted with cold efficiency by men who read poetry and listened to string quartets afterwards.
They turned upside-down the paraphernalia of progress to achieve it. Architects planned the camps – an interesting challenge, presumably, for no one had designed this kind of concentration camp before. Sewage engineers surveyed them, installing drainage ditches in the marshland ' and effluent treatment plants to avoid polluting local rivers. Rail officials timetabled the steady influx of trains to Birkenau, selected by Himmler for its good railway links.
This was extermination on an industrial scale and it involved huge numbers of people. Neighbours and employers reported Jews to the Gestapo. Bureaucrats processed notices of deportation. Postmen served them. Railway staff marshalled their departure. Others drove the trains and manned the signals. It was all logically and legally planned in an inversion of all the values on which human civilisation had been built. So perverse was it that Hitler ordered the collection of 200,000 Jewish artefacts, which were photographed and catalogued to be displayed at the end of the war as a trophy case of archaeological remains. It was to be called The Museum of an Extinct Race.
The extent to which the German population not only knew about the Holocaust but also supported it is a question which another of the teachers, Peter West, of King Edward VI College in Stourbridge, regularly raises with his A-level students. He points them to Daniel Goldhagen's controversial 1996 book Hitler's Willing Executioners, which suggests that anti-semitic attitudes were deep-seated in Germany and argues that the Nazi state was possible only because it was backed by ordinary people. "There's a matter-of-factness and lack of emotion about the place," West says, peering round perplexedly. "Were they proud of what they were doing? If so, why did they blow it all up? Did they think the world wouldn't find out? I don't know the answer."
But he offers the example of the city of Wurzburg, where surviving files suggest that, contrary to popular belief, the Gestapo was not omnipotent, with agents in every cranny of German society. "Wurzburg had just 28 Gestapo officers for a population of a million people. The vast majority of Gestapo investigations were started in response to information provided by ordinary Germans," he says.
An edifice of lies supported the whole ghastly enterprise. The camps were presented as places of resettlement. Families were told to pack a suitcase and given lists of essential clothing and goods. When they arrived, the suitcases were taken from them, and their careful contents later casually ransacked and sorted to be sold. Some knew then what this meant. "The cherished objects we had brought with us thus far were left behind in the train, and with them, at last, our illusions," wrote one survivor, Elie Wiesel. But others persisted in hope, even as the Nazis persisted in their lies. At the end of the long walk from the railway ramp, the condemned were ushered into a subterranean dressing-room. There were numbered hooks for the clothes. "Remember your number for when you come out," the guards shouted. "Children, fasten your shoes together by the laces so they don't get separated when you come out." They would, of course, be easier to sell if the pairs did not become separated.
Even inside the killing-room the deceit persisted. There were fake shower heads in the ceiling to maintain the pretence that this was a place of cleansing until the very final minute. Then cyanide pellets were dropped through holes in the roof. Even on Nazi invoices, now in the Auschwitz museum, the mendacity continued: new supplies of Zyklon B were billed as "material for Jewish resettlement".
When the gas cleared, groups of press-ganged inmates came in to shift the corpses, pull out any gold teeth and shave hair. These men, known as sonderkommando, were better-fed and worked at their grisly task for three to four months; then they, too, were killed: they had seen too much.
The hair was stored in a room above the furnaces to keep it warm in the piercing cold of the Polish winter. No such luxury was permitted the camp's inhabitants, but then hair was worth something – half a mark a kilo. The textile industry used human hair to line socks and gloves for submarine and railway workers and make thermal blankets. There was a grim efficiency about it. The human ash from the furnaces was stored in four purpose-built pits, which remain today, from where it was taken to be spread on local farmer's fields.
Some of the teachers with whom I am travelling are tasked with communicating all this to far younger children than Peter West's sixth-formers. Amy Barlow, of Great Sankey High School in Warrington, teaches the Holocaust to 13-year-olds, as well as organising the school's Holocaust Memorial Day in which pupils as young as 11 participate. "Many find it hard to grasp," she says. "They ask: 'How could anybody do that? How did they get away with it? Why did no one stop it?' Adolescents have a very black-and-white view of the world. They say things like: 'I'd have just refused to obey orders.' So I ask them: 'Have you ever seen anyone being bullied? Did you do anything about it?' I tell them how Hitler was very persuasive – that he said he would create jobs, rebuild the economy and bring back Germany's glory. Then I ask what they think about the BNP, which some of them support, and all its rhetoric about foreigners taking our jobs. And they are shocked when they see the link."
Truth continues to be an elusive concept in Auschwitz. The place has begun, literally, to fall apart. The brick-built barracks of Birkenau are out of bounds now because they are unsafe; the museum authorities have replicated one of the Aushwitz II bunk barracks inside an Auschwitz I building so that visitors may imbibe the atmosphere without venturing into the dangerous Birkenau barracks. Workmen are replacing rotten wood in one of the watchtowers. There is much debate about whether maintenance is appropriate to memorial.
Even more so when, because the Nazis set off explosives in the four purpose-built crematoria at Birkenau, the original gas chamber in Auschwitz I – which the Nazis had converted to a bomb-shelter – has been transformed back into a gas chamber by the museum authorities. The chimney has been reconstructed, along with the furnaces and the scoop-shaped trolleys which could thrust two or three bodies into the fires at a time. The place could burn 340 bodies in 24 hours; the destroyed death chambers of Birkenau were built to incinerate 5,000 corpses in a day. "I don't know how I feel about the idea of replica in a place like this," says one of the teachers as we go in. The binding together of memory is a curious business.
But that is the task with which my fellow travellers are charged. At present, they invite survivors to talk to their school assemblies. But even those survivors who were just 14 when they were incarcerated in Auschwitz – they had to pretend to be 18 to avoid immediate direction to the gas chamber – are well into their eighties now. Soon there will be no first-hand testimony available, and it will be our teachers who decide what is remembered and what is forgotten.
"The unit I have put together on the Holocaust is the most important thing I have done as a teacher," says Amy Barlow, thinking of the impact it has had on her 13-year-olds back in Warrington. "We look at the history of anti-semitism, the slow building of feelings against the Jews with the Nuremberg laws, the devising of the Final Solution, the resistance to the Holocaust, how it ended and then we ask whether it could happen again. At the end I play devil's advocate and ask 'Isn't it time to move on?'
"The girls get angrier than the boys," she muses. "In the immediate aftermath of the subject they change in their attitudes to one another. Often, kids can be quite cruel and that softens – for a while, at any rate. They can get very reflective. They seem to be grateful for their lives."
It is not only children who need to learn such lessons. We all make choices at every moment in our lives. They are part of building a world in which another Holocaust might, or might not, happen. In the end, history means little if it leaves our present unchanged.
For more on the Holocaust Educational Trust: het.org.uk