For those going the DIY route, whether by bus or train, the route planning website e-podroznik.pl is a valuable resource. Frequent buses depart for Oświęcim from the main bus station (Kraków MDA, ul. Bosacka 18); most stop at the Auschwitz Museum entrance (called 'Oświęcim Muzeum'), but not all, so make sure beforehand otherwise you may end up at the Oświęcim bus station which is at the other end of town. The journey takes 1hr 20-40mins and costs 12-15zł. Bus schedules can also be checked at rozklady.mda.malopolska.pl.
Frequent, almost hourly trains also run between Kraków and Oświęcim, with a journey time of 1hr 45mins - 2hrs 15mins and a cost of about 9zł; note, however, that early trains to Oświęcim can be eerily crowded, particularly on weekends. Train schedules can also be checked at rozklad-pkp.pl.
The Oświęcim train station (ul. Powstańców Śląskich 22) lies strategically between Auschwitz I and Auschwitz II-Birkenau, which are 3km apart. Local bus numbers 24-29 stop at Auschwitz I; buy a ticket (under 3zł) from the nearest kiosk. Museum buses regularly shuttle visitors between the two camps, or catch a cab for 15zł. Waiting minibus taxis run by Malarek Tour (+48 605 31 50 77) can take you back to Kraków from either camp - a group of eight would pay about 30-40zł/person.