According to auschwitz.org:
The second part was the Birkenau camp (which held over 90,000 prisoners in 1944), also known as "Auschwitz II" This was the largest part of the Auschwitz complex. The Nazis began building it in 1941 on the site of the village of Brzezinka, three kilometers from Oswiecim. The Polish civilian population was evicted and their houses confiscated and demolished. The greater part of the apparatus of mass extermination was built in Birkenau and the majority of the victims were murdered here.Various sub-camps were also built, but many of these have been demolished.
Birkenau was the largest of the more than 40 camps and sub-camps that made up the Auschwitz complex. During its three years of operation, it had a range of functions. When construction began in October 1941, it was supposed to be a camp for 125 thousand prisoners of war. It opened as a branch of Auschwitz in March 1942, and served at the same time as a center for the extermination of the Jews. In its final phase, from 1944, it also became a place where prisoners were concentrated before being transferred to labor in German industry in the depths of the Third Reich.The endless rows of electrified barbed wire fencing reinforce the horror and enormity of the site. The railroad tracks in the first photograph show where trains with prisoners packed into box cars were unloaded. The women, children, and elderly were separated and almost immediately marched off to the gas chambers. Their possessions and clothing were sorted by slave workers. The victims were gassed and then inspected by other slave workers. They removed gold from their teeth. Then the bodies were loaded by more slave workers into ovens (crematoria).
Today, few of the wood barracks remain standing. When Soviet troops approached western Poland in December 1944/January 1945, the SS sent remaining prisoners west on forced marches, during which thousands died. Then they burned the wood barracks and blasted the gas chambers and crematoria. Stark chimneys are all that is left of the barracks, while the gas chambers have been left as piles of brick and rubble.
From http://www.pbs.org/auschwitz/40-45/liberation/:
As the Soviet army approached and the end of the war came closer the vast majority of Auschwitz prisoners were marched west by the Nazis, into Germany. Those few thousand remaining were thought too ill to travel, and were left behind to be shot by the SS. In the confusion that followed the abandonment of the camp, the SS left them alive. The prisoners were found by Soviet forces when they liberated Auschwitz on January 27, 1945.
Vasily Gromadsky, a Russian officer with the 60th Army liberating Auschwitz recalls what happened.
"They [the prisoners] began rushing towards us, in a big crowd. They were weeping, embracing us and kissing us. I felt a grievance on behalf of mankind that these fascists had made such a mockery of us. It roused me and all the soldiers to go and quickly destroy them and send them to hell."A couple of buildings still stand. Tens of prisoners slept on these bleak benches in filth and sickness.
Some primitive latrine buildings were built to reduce disease. The former gas chambers were piles of brick, which I did not photograph. The ovens were also destroyed by the fleeing Nazis just before Soviet troops arrived. A replica of one oven has been built, but I did not photograph it. It is amazing to me that as the Nazi 1000-year Reich collapsed, the Nazi authorities tried to cover up the physical evidence of their atrocities, as if that would be possible considering the magnitude of their industrial-scale death camps.
Dear Readers, please remember that these horrors were created by the same urbane and sophisticated society that previously brought us Martin Luther, Goethe, Schiller, Beethoven, and Bach. The camps demonstrated depths of depravity previously unimagined in cultured and civilized Europe. But evil lives very close below the surface of most societies. Government-sponsored and societal-approved brutality is insidious because ordinary people begin to believe that atrocities imposed on others is "normal" or quite all right. Consider how we treated African-Americans as late as the 1960s in the American South. It was "OK" to lynch blacks. And most people cannot or will not fight against the prevailing norms in their society - they just want to fit in. Considering the despicable hate talk we heard during the 2016 election in USA, remember the lessons of Auschwitz when you hear calls to imprison or deport Muslims and Mexicans, or when the specter of anti-semitism and racial superiority rears its ugly head again. Is the United States descending into this kind of tribalism?
The square photographs were taken on Kodak Tri-X 400 film with a Rolleiflex 3.5E with 75mm f/3.5 Xenotar lens. I developed the film in HC110 developer at dilution B for 4:30 minutes. I scanned the negatives with a Minolta Scan Multi medium-format scanner (approx. 2000 vintage). Click any picture to enlarge it to 2,400 pixels wide.