Auschwitz-Birkenau, located in Oświęcim, Poland, is one of the most infamous concentration camps from World War II. These are located about 70 kilometers (43 miles) west of Kraków, accessible by buses and trains. Established by Nazi Germany in 1940, it became the largest site of mass extermination during the Holocaust. Over 1.1 million people, primarily Jews, were murdered here, along with Poles, Roma, Soviet prisoners of war, and others. Today, it serves as a museum and memorial site.
It was a network of German Nazi concentration camps and extermination camps. This place showcases all the atrocities during the nazi regime. You can reach here in an hour from Krakow. It will take 3-4 hours to have a look at the whole camp, though it is well organised and one can feel the pain and sentiments that many polish people and jews experienced. This is a must visit for historians.