Survivors of the Holocaust will gather in Auschwitz on Monday to mark the 75th anniversary of the camp's liberation.
They will be joined by world leaders and dignitaries including the Duchess of Cornwall and the Mayor of London, Sadiq Khan, to remember the 1.1 million people who were gassed or shot by the Nazis there during the Second World War.
Among them will be Alberto Israel, a ninety-three-year-old Jew now living in Brussels.
He was detained at the camp in German-occupied Poland in 1944 when he was 17 years old.
He told me: "For all the people that survived, all those I've spoken to, the most horrible thing for us, the worst punishment of all are the nightmares. I can't stop them, even today."
He cries as he tells us: "They threw babies that were alive into the oven. And when you've seen that and you ask me whether I can sleep. Sleep? How can I sleep?"
Mr Israel lost his family to the Nazis.
His parents and one brother were killed at Auschwitz - the concentration and extermination camp in Poland which became the most potent symbol of the Holocaust.
Men, women and children were starved, experimented on and murdered.
It was a place where age was no barrier to the brutality.
Albert Reiss shows us a photo of him, aged three, along with four young cousins.
All four were killed by the Nazis.
He only survived Auschwitz because a Catholic couple in Brussels took him in when he was a toddler and pretended he was one of their own.
The now eighty-year-old was one of the enfants caches - or "the hidden children".
"The couple and the people that were doing this, they could be condemned at the very minimum to go to jail but normally they were simply shooting them," he continued.
"They put them against the wall. They were really risking their lives.
"And even the life of their girl because they had a girl of fourteen years old. So I think you understand the risk they were taking."
When Mr Reiss was returned to his mother after Brussels was liberated in 1944 he didn't know her.
His father had been killed at Auschwitz - a place Albert has always refused to visit.
"Some people say forgive what happened during the war. I say I will never forgive. I can't, I cannot do that. I cannot forget. This is something I always remember," he said.
And remembering is what they will be doing at Auschwitz tomorrow.
Survivors reliving painful memories as they return to a place where so many lost their lives.
But in doing so, the survivors hope they will also be warning future generations of where political extremism can lead.
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