Located just at the exit to Auschwitz is the museum about the former concentration camp. There is also a car park, and it's possible to buy tickets for guided visits or audio guides for the two camps. Apart from these options, however, it's all free to visit.
Our guide was very passionate about the subject and that enabled me to gain a good understanding about the atrocities that took place at these sites. Once past the sadly famous gateway, I noticed the atmosphere felt very oppressive. If feels a bit like time has come to a standstill here. The stone buildings are encircled by terrifying barbed wire fences, and each had its own specific purpose (medical experiments, prison, sleeping barracks …). What shocked me most during the tour were the piles of human hair and shoes.
Definitely somewhere you absolutely have to go to when visiting Poland, as a way of commemorating what took place.