Visiting Auschwitz/Birkinau was top of the list for me when visiting Krakow. I visited Dachau over…read more10+ years ago which was the very first concentration camp but Auschwitz-Birkenau was a scale larger and meant for extermination. It certainly was eye opening, upsetting at times and unimaginable in horrors.
Booking online ahead was important to secure an English tour on a date/time that worked for my schedule. Note there were two tours available: (1) normal took 3.5 hours or (2) 6 hour educational. I booked mine about one month ahead of time (March visit for me) but tours could sell out sooner depending on the season.
After booking, recommendation was to arrive min. 30 minutes prior to allow time to clear security. No large backpacks were allowed (though inconsistent in applying the rule) and had to be checked in across the street.
I suggest taking the Lajkonik bus from Krakow (22zl each way) which dropped us off right in front of the main museum entrance. It was a better option in my opinion versus taking the train and then having to walk (20+ minutes) or taxi. Return buses can quickly fill up so book a seat online for a time slot at least 1/2 hour after your tour ends (to give you enough time to get back from Birkenau). However, if you miss your scheduled bus or want to leave earlier then the online ticket cannot be reapplied.
Tours left every fifteen minutes which seemed a bit rushed initially as some tours started backing up or speaking over each other. However, after the first half hour the spacing finally improved and it was a better experience. Our guide was an excellent source of information and really helped us understand the importance of every stop along the way. Photos without flash were allowed but the guide will inform when it's not allowed.
The total tour was 3 hours, 30 minutes across both camps. ~2 hours to complete Auschwitz, a break and bus ride in between, and ~1 hour to complete Birkenau.
I could say more but it's a must to experience for yourself.