I decided that I could not go to Krakow without visiting these two historic, Nazi death camps from WWII.
Auschwitz was established in 1940 to house Polish Political Prisoners. Later the Nazis began to deport people from all over Europe including Jews, Soviet prisoners-of-war and Gypsies. The original buildings were expanded and often floors added. I like to be able to walk, silently, viewing the blocks that were open for special exhibitions. Several were dedicated to the Jews from different countries like France and the Netherlands. Others were dedicated to the history of the camp and transporting the prisoners. Most moving to me were the photographs, the room filled with displays of discarded shoes and pieces of luggage, pictures of children and the cells filled with beds or mattresses. You could see where some were shot, where others were hanged and where most were cremated.
Birkenau, a short distance away, is much larger and you can see the main gate, visit some of the wooden and brick barracks.
There are group/bus tours available, but I chose to hire a driver through my hotel and do it privately. In this way I was able to walk through both sites on my own using a purchased guide book. The company was Around Krakow. They also can do airport transfers that can be scheduled before you arrive.
Because of the recent anniversary of the liberation of Auschwitz there has been a large influx of visitors. So not to be turned away at the gate, I would suggest booking your tickets in advance at Visit Auschwitz before you go.