Auschwitz I (Main Camp) Concentration Camp

Konzentrationslager Auschwitz, in particular KL Auschwitz I (Stammlager), KL Birkenau (Auschwitz II) and KL Monowitz (Auschwitz III) - a complex of German Nazi concentration and extermination camps, operating in the years 1940-1945 in Oświęcim (German Auschwitz) and nearby localities; symbol of the Holocaust, also known as the "factory of death".
As the only German concentration camp, it was inscribed on the UNESCO World Heritage List (1979) under the name Auschwitz-Birkenau. German Nazi Concentration and Extermination Camp (1940–1945). The Auschwitz-Birkenau State Museum in Oświęcim (1947) was established in part of the camp as a monument and cultural institution documenting German crimes in occupied Poland.
The names Auschwitz, Birkenau and Monowitz are the German equivalents of the Polish names Oświęcim, Brzezinka and Monowice, used after the German aggression against Poland in 1939 and the annexation of these lands by the Third Reich.
In 1940, the German authorities established a camp in these areas intended initially for the detention of political prisoners and opposition, mainly Poles. It was then gradually expanded, eventually becoming the main site for the mass extermination of approximately 1.1 million Jews from all over Europe, as well as 140–150,000 Poles, approximately 23,000 Roma, approximately 12,000 Soviet prisoners of war and victims of other nationalities.
pl.wikipedia.org/wiki/Auschwitz-Birkenau
auschwitz.org/zwiedzanie

Tickets are free and are collected at the ticket office, in front of the entrance to the Auschwitz I Museum.
Sometimes the number of visitors is so large that it may turn out that they do not issue tickets on a given day, so if you want to be sure of entry, it is best to order such a ticket online in advance.
You must also have an identity document with you.
There is a bus between the camps Auchwitz and Birkenau.

Former polish military terrain and later used by the Germans to murder million of people