The public was not allowed inside this building. It's where medical experiments were conducted. Experiments such as forced sterilizations. Experiments on twins to see how one would react to induced, deadly diseases. Experiments on the effects of starvation. Those subjects who weren't killed during the experiments almost always ended up being executed.
The actual Auschwitz gas chamber. Where thousands of people were gassed. An assembly line.
Auschwitz had been an old barracks, and it wasn't large enough to accommodate the Nazis' purposes. A couple kilometers away, Birkenau was custom-built.
The infamous railroad tracks. This is where arriving prisoners were sorted by Josef Mengele. Some were sent to barracks, to work as slave laborers. Some were chosen for medical experiments. Some were sent immediately to be gassed.
If you were a "lucky" woman, capable of slave labor, you got sent to live in barracks such as these. With other women piled on top of you. Freezing, ill, dying. For as long as you could hold out. If you didn’t die, once you were too weak to be of purpose you were shot. Or gassed.
Before they left, as the Allied armies approached, the Nazis tried to cover their tracks, including by imploding the two Birkenau gas chambers. Hundreds of thousands of people were murdered in this small building. Hundreds of thousands of people were gassed to death in just two small buildings.
Pools of ash, a short walk from the gas chamber.