Other than the camps there is nothing else to do in Oswiecim. It's basically a factory town with a huge industrial facility right in the middle of the city. I'm not even sure what it produces, but your time is better spent in Krakow. Auschwitz is a important place to visit and I'm glad I did, and recommend others do it as well, but it made me sick to my stomach and I was glad to get as far away from it as possible. The notion of staying overnight in a city where millions of people were slaughtered is not something I would recommend. There is a good reason why most everyone only visits for the day.