By Matthew Collin at Auschwitz in Poland.
People come from all over the world to see the place where the largest mass murders in history were committed.
As they file past huge glass cases containing piles of intimate possessions like shoes, suitcases, spectacles and even false limbs which were taken from people before they were killed by the Nazis, some become distressed and a few burst into tears.
More than a million people were systematically exterminated at the Auschwitz-Birkenau death camp complex in southern Poland during World War Two, and it has become a worldwide symbol of the horrors of genocide.
Most of those murdered here were Jews, as part of the Nazi project to annihilate European Jewry, but Poles, Roma gypsies and Soviet prisoners also died.
Metal canisters which once contained the Zyklon B gas that killed them are also on display.
"I knew a bit about this, but to see it in reality is shocking; just an awful example of how cruel people can be," said a teenage girl who had travelled to Auschwitz from Estonia.
Some visitors were shocked by the sheer size of the camp, and the way the Nazis coldly industrialised the extermination process.
"In our times, something like this is unbelievable," said a Polish woman who was visiting with her family.
"You have to see it to believe that people can do such things to other people."
Ravages of time
But the Auschwitz-Birkenau Foundation, which oversees the site, has warned that the memorial is under threat from the ravages of time.
It is appealing to governments worldwide for money to underwrite the annual costs of preservation and maintenance, which amount to more than $5mn, and to set up a perpetual multi-million-dollar fund to secure the future of the site.
Because much of the camp was hastily constructed by prisoners during World War Two, and not built to last, many of the gas chambers, cremetoria and barracks are now seriously deteriorating and are already closed to visitors for safety reasons, while others have collapsed completely.
"These buildings were not built here to stand for 60, 70 years," explained Pawel Sawicki, a spokesman for the Auschwitz-Birkenau Museum.
"They were built by prisoners who were not engineers, who used bad building materials and who were themselves exhausted, hungry, beaten.
"We can't just fence it all off and show a multi-media exhibit, because people come from very long distances to see the authentic evidence of genocide, so our challenge is to keep these buildings standing and open."
In the museum's preservation centre, a technician was carefully repairing a pair of shoes which once belonged to an Auschwitz inmate.
The scientific team at the former concentration camp uses modern technology to painstakingly restore documents and personal items like clothes, suitcases and even toothbrushes - poignant symbols of individual tragedies.
"We have a huge problem with toothbrushes because they're made of early 20th century plastic, so we're establishing a research programme to work out how to preserve them," said Sawicki.
Sawicki explained that a key purpose of the work is to collate personal information which could be passed on to relatives of those who died.
"We've found all sorts of things inside shoes: notes, newspaper clippings, once even a child's mathematics test," he said.
More than a million people visit Auschwitz every year, but the camp is not just a tourist attraction; it is also a mass grave.
The ashes of gassed and burned bodies were dumped all around the site.
"You see that green space?" asked Sawicki, pointing to an attractive little lawn outside the camp's main gate.
"It's also a burial ground. Every piece of land here is actually a witness to human tragedy and suffering."
Last year, the camp suffered another blow when the famous sign at the main gate, which reads 'Arbeit Macht Frei' ('Work Makes you Free'), was stolen late at night, although it was recovered within days.
More than 60 years after Auschwitz was finally liberated, the number of survivors of the camp who are still alive is inevitably getting smaller.
As the voices of the eyewitnesses fade into history, it becomes even more important to preserve the camp, so future generations can understand the reality of genocide, said Sawicki.
"In a few years' time, there will be no more survivors," he said.
"We need to find a way to teach the history of this place when they are no longer with us."
Since the museum was established in 1947, the vast majority of the funding has been provided by the Polish government.
After the Auschwitz-Birkenau Foundation made its survival appeal, Germany, Austria and the US committed significant amounts to the long-term preservation project, but more is still needed.
Visitors to the camp are insistent that it must survive, not only as a memorial, but also as a vital history lesson.
"It makes you relive the past, so it doesn't happen again in the future," said one French tourist. "It's really important for future generations to come here."
A young student, sitting in contemplative silence outside the museum, had clearly been disturbed by what she had seen inside.
She summed up what it meant to people of her generation.
"Of course we learned about the Holocaust at school," she said.
"But it's only now that I understand how horrible it really was."