It doesn’t matter how much you prepare for it. It still takes you by surprise. As the great-granddaughter of a woman who was murdered in Auschwitz, I am meeting the granddaughter of a man who drove Jews to their death. I’m lost for words.

I never got to meet my grandfather Ludvig, who survived the Holocaust, or his mother Rachel. They were put onto a cattle cart to the Auschwitz death camp in 1944. Ludvig, who was about 15 at the time, was separated from his mother and sent to another concentration camp. But Rachel was tortured, gassed and murdered.

I grew up hearing so many stories about them, and spending time with other Holocaust survivors in my family in Australia. They were at the forefront of my mind when I found myself in Germany interviewing Cornelia Stieler.

Cornelia’s grandfather was the main breadwinner in a household with very little income. He originally worked as a coal miner, but after a near-fatal accident which left him trapped under coal for two days, he decided to do something else. Things turned around when he eventually got a job at Deutsche Reichsbahn as a train driver. Cornelia’s mother used to speak of that achievement with pride, saying getting the job was “the chance of a lifetime”.

At first, he was transporting goods for the war effort. But it soon turned into something more sinister. “I believe that my grandfather served as a train driver, commuting between the death camps. He stayed in Liegnitz, now Legnica, in a boarding school, so there was a certain separation from the family and between the death camps.”

Cornelia says that when her grandfather first started the job, he didn’t know what it would become. “I think my grandfather saw a lot of horrible things and didn’t know how to get out of this work, didn’t know how to deal with it.”

After training as a family therapist, she delved into her past and tried to understand him better. She tells me she started asking: “At what point was he a perpetrator? Was he an accessory to perpetrators? When could he have left?”

At this point, my mouth is dry. My heart is racing. Listening to all of this feels like an out-of-body experience. All I can think about is how her grandfather drove trains into Auschwitz, and that’s how my grandfather and great-grandmother ended up there. I’m thinking about all my other relatives – cousins that I know existed but know nothing about – who were murdered in Auschwitz too.

“If I were any younger, I think I’d feel a strong hate towards you,” I tell her, fighting back tears. “But I don’t because saying all of those things must have been really difficult to admit.”

“Give me your hand,” Cornelia says, also welling up. “It’s important. Your tears, and my touch, are touching me… My grandfather was a train driver in Auschwitz. What can I say? Nothing.

“I can’t apologise, it’s not possible,” she adds, implying the crime is too grave. “My grandfather felt very, very guilty, and he died with his guilt.” Cornelia thanks me for my openness and says there’s a need to fully uncover the history.

Then she says something you might not expect – that some Germans from Schönwald, where her family came from, had reacted angrily to her research. The now Polish town renamed Bojków, some 100km from Kraków, hasn’t come to terms with its Nazi past.

Cornelia explains that originally, the town was against the ideology of the Nazi Party, but over time, became consumed by it. Hitler saw Schönwald as a model village – an Aryan village in a land of Slavs. He was hoping that a “fifth column” of ethnic Germans there would become a useful aid in the military.

It was the site of the Gleiwitz incident – a false flag incident staged by Nazi Germany in 1939 to justify the invasion of Poland, one of the triggers of World War Two. And in 1945, towards the end of the war, it was the first German village to be attacked by advancing Soviet forces.

But just before that, it was the scene of one of the Nazis’ so-called death marches.

As Soviets approached Auschwitz, Hitler’s elite guard, the SS, forced around 60,000 prisoners there – mostly Jews – to move further west. Between 19 and 21 January 1945, one of those marches passed through Schönwald. In below freezing temperatures, the prisoners were dressed only in their thin striped uniforms with just wooden shoes on their feet. Those who collapsed from starvation and exhaustion were shot.

Those who survived were put onto open cattle cart trains heading further west, usually to other concentration camps, like Buchenwald. The Nazis wanted to hold onto their slave labour – even at this point, some still believed in an ultimate triumph of the Third Reich.

A local history and religion teacher, Krzysztof Kruszynski, takes me to the main street where the death march passed. People wait to catch their bus outside the main church on Rolnikow Street – known as Bauer-Strasse in German times. He points to ground, and tells me these are the original cobble stones that the prisoners had to walk on.

“It is a silent witness of the death march,” he says. “But the stone cannot talk.”

This history has been buried until now – partly because Germans from Schönwald were forced to flee after the Soviet attack that came soon after and Poles resettled the village. One German-Polish woman in her 80s, Ruta Kassubek, told me how drunk Soviet soldiers had stormed her family home and murdered her father. But there’s another reason: an active suppression of the past.

It didn’t surprise me that some Germans had responded negatively to Cornelia’s research. Germany prides itself on its Erinnerungskultur, or culture of remembrance: mandatory Holocaust education, museums, memorials. But many see that as the job of state and government. And while they’re happy enough to face the past in the abstract, it’s harder to deal with their own family history, says Benjamin Fischer, a former Jewish student leader and political consultant. He calls it the “deindividualisation of history”.

A study by Bielefeld University found that a third of Germans believed their family members helped save Jews during the Holocaust. That’s “ridiculous”, says Benjamin, and “statistically impossible”.

On the ground in Bojków, 80 years after the death march, things are changing. Last week, a delegation of Germans, Jews and Poles, including local authorities, schools and emergency services unveiled a new memorial commemorating those who died in the town’s death march.

Cornelia and Krzysztof were there. For Cornelia the history is deeply personal. She is convinced that studying and remembering it is key to understanding how society could change so rapidly. And I’m grateful for it. Their work and passion gives me hope in a world of rising antisemitism – as I try to keep the memory of how my family came to be murdered alive.

The people of Schönwald believed their town lay at the pinnacle of high culture and spirituality. But then it “folded into immorality”, Cornelia says. “This is a development that we need to understand… They weren’t solely good or evil. People can go into jobs with good intentions but very quickly, [find themselves] on the wrong side.

“We can’t change the past. We can’t turn back time. But it’s important to talk about this, to remind people of what happened, to remind people of what humans can do to one another.”