Everyone has heard haunting stories about the concentration camps, but nothing can convey the feeling of visiting Auschwitz.

In peak war time there were three Nazi concentration camps around Oświęcim (Auschwitz in German), a town in German-occupied Poland.

Now only two remain open to the public to show the horrendous ordeals the prisoners went through in the Nazi concentration camps – Auschwitz-Birkenau and Auschwitz.

I was invited to join the Holocaust Educational Trust on their annual visit to these sites with more than 200 other visitors from across the country.

The first camp we visited was Auschwitz, one hour from Krakow airport.

Originally the site was used as a barracks but when the Nazis invaded Poland the empty buildings became the first concentration camp in that area.

As we made our way under the 'Arbeit Macht Frei' sign at the gates, the persecution was revealed in greater detail.

The sign translates as ‘work makes you free’ – a sick joke by the Nazis, as nobody was supposed to leave the camp alive.

More likely than not you have heard horrifying stories from survivors or other Holocaust educators but the true extent cannot be described without seeing it for yourself.

Many of the cell blocks now contain masses of belongings taken from the prisoners.

Wash pots, suitcases with names on them, and, most disturbingly, children’s toys and a mountain of hair shaved from female prisoners used to make bags.

These prisoners did not have a choice and millions did not get the chance to live their lives.

By 1941 the Nazi genocide had stepped up and Auschwitz became too small due to the sheer number of prisoners arriving from across occupied countries.

Two miles away is the site of Auschwitz-Birkenau – a camp with an area covering an area the size of 250 football pitches.

The scale of Birkenau is overwhelming, and harrowingly it was built for the sole purpose of murdering Jews.

The iconic railway tracks and entrance dominate the bleak and desolate camp. It is difficult not to see the brick watch tower from any part of the site.

Rabbi Barry Marcus of London’s Central Synagogue revealed that only around 25 per cent of prisoners were taken to the camps to work, while 75 per cent were sent straight to the gas chambers.

His words "in Birkenau it is not what you see but what you don’t see" resonated as we walked through the cold April air across the camp.

Towards the end of the war, the Nazis tried to hide what happened in Birkenau and blew up the two biggest gas chambers and crematorium, the rubble of which is still there.

Why keep piles of rubble? Due to the number of people sent through the crematorium, sickeningly, there are probably ashes in the destroyed buildings.

Most Jewish prisoners never entered in the camp’s records as they were killed upon arrival.

Though it has been recorded that around 1.1 million Jews were killed there, it is impossible to give precise figures for the numbers of people sent to Auschwitz.

Rabbi Marcus also said before the war broke out there were more than three million Jews in Poland. Now there are less than 5,000.

It is hard to think something so shocking happened not even 70 years ago, and without visiting the sites yourself it is difficult to fully understand what the prisoners went through.

At the end of the visit around Auschwitz-Birkenau Rabbi Marcus gathered us together and sang a prayer remembering all those who were murdered there.

The group fell silent. Rabbi Marcus’ voice echoed across the camp and his words ‘time will never let us forget’ has been etched into my mind.

The weather turned cold and it got darker. Students placed candles on the memorial to remember those persecuted during mankind’s darkest hour.

What happened at these camps should never be forgotten. Yet persecution of religious groups and other innocent people still goes on in the world today.

Has mankind not learned?