Peter Josep Snep still talks at schools about the horrors he experienced at Sachsenhausen concentration camp, but 65 years after its liberation he is one of a dwindling number of survivors.
"The schoolteachers tell me that normally the kids won't keep still for five minutes," the frail 89-year-old Dutchman says. "When I tell them my story, they don't make a peep for an hour."
Although not an extermination camp devoted to murder on an industrial scale, all of which were outside Germany in Nazi-occupied Eastern Europe, concentration camps such as Sachsenhausen were still places of unspeakable horror.
Just north of Berlin, it covered an area the size of 800 football pitches, imprisoning 200,000 real or imagined opponents of Nazism from within Germany and all over Europe between 1936 and 1945.
Snep made it out, shipped back home where he went into hiding, but tens of thousands of others were not so lucky, dying from hunger, disease, worked to death or murdered in cold blood, or on a forced "death march" in April 1945.
"I can't believe I'm sitting here today," Snep, holding back tears, said this month, one of around 300 survivors attending ceremonies marking 65 years since Sachsenhausen's liberation.
Other concentration camps on German soil like Ravensbrück, Buchenwald and Bergen-Belsen have also been marking the anniversary of their liberation. Dachau near Munich in southern Germany does so on May 2.
People like Snep are a vital tool to ensure that Germany's dark past is not forgotten, particularly for schoolchildren, achieving what text books fail to do - making history come alive.
"Listening to a survivor is something really special, it's incomparable," said Robert Sigel, a teacher at a grammar school in Weimar, a city in central Germany proud of its cultural heritage that the Buchenwald camp, high up on a hill, overlooks.
"Pupils ask questions, basic moral questions that are important for young people, like what would I have done, and why did no one help," Sigel, who is involved in government efforts to coordinate the teaching of Nazi history, told Berlin's Inforadio.
But prospects indicate that interest will remain high once camp survivors are no longer around.
Buchenwald, for example, has seen visitor numbers rocket from around 130,000 two decades ago to around half a million last year. Sachsenhausen's visitor numbers have grown from 168,000 to 400,000 in the same period.
Dachau last year opened a new centre to accommodate its 800,000 annual visitors from all around the world. Neuengamme near Hamburg has also just got a makeover, while Sachsenhausen too is expanding its offering.
Instrumental in this has been millions of euros in government money in recent years to patch up the crumbling camps and provide more exhibits to inform visitors - something which is a relatively recent phenomenon.
"Since the voices of witnesses will one day be silent, it is essential that memories of the past are kept alive, particularly at memorials and museums, so that our historical responsibility is firmly anchored in the conscience of future generations," Culture Minister Bernd Neumann said this month.
According to Günter Morsch, director of the body in charge of Sachsenhausen and Ravensbrück, it was only after the unification of East and West Germany in 1990 that the camps were "discovered" as a way to keep memories alive.
Buchenwald, Ravensbrück and Sachsenhausen had all been in East Germany. After 1990 the government moved to transform places "instrumentalised" for communist propaganda into historical sites, Morsch said.
This process attracted international interest and then sparked efforts by camps in former West Germany like Bergen-Belsen and Dachau to improve, and for the government to assume more responsibility for their upkeep.
"In Flossenbürg (in former West Germany, near the Czech border) there was nothing, I can remember. You went there, slotted five deutschmarks into a machine and got a brochure," Morsch says. "Dachau was run by the Bavarian department for castles, gardens and lakes."
The result is that the former camps are chilling places.
At Sachsenhausen visitors can see a cellar where corpses awaited incineration, the remains of a small gas chamber and execution area where 13,000 Soviet prisoners of war were murdered in 10 weeks, as well as exhibits on medical experiments and partially reconstructed prison huts.
Another is one that brings back personal memories for Snep, the area where he, his father and around 100 other emaciated prisoners were forced to march all day, every day, on different surfaces in order to test German boots.
"The 'shoe commando' was basically a death sentence," Snep remembers. "If you collapsed you got the 'Genickschuss'," shot in the back of the neck by an SS guard.
"Every day 10 or 12 didn't make it."