Advance tickets for museums in Krakow recommended?

We were on the Central Europe Tour last summer. Definitely book ahead for the Schindler Factory. My impression was that it does sell out. We chose the English guided tour.
It seemed like the Salt Mines didn’t necessarily need to be reserved ahead of time, but we didn’t do that one, so I can’t say for certain. I think some tour mates went and it seemed rather spur of the moment.

I looked at Discover Crakow, which is the company I used to book a tour to Auschwitz back in April. They display a "Likely to sell out" banner on their salt mine tour package. Next day tours for some departures are still available, but it's safe to assume that demand will be higher in June.

You didn't mention Auschwitz, but note that some days the first week in June are no longer available for their packaged tours, and no availability for May.

They show only limited availability for Schindler's for the next couple of days. Of course you can look at the official provider for Schindler's, as well as other tour companies.

If your RS tour schedule is determining when you are available, it might be best to book ahead.

The Schindler Factory was sold out the day I visited in the summer of 2018, and there are more people traveling now. Advance-purhase tickets for Auschwitz were sold out for the next eight days.

I don't know about the salt mine.

Thanks all.

Visiting Poland 6/2/2024-6/15/2024.
Schindler Museum: Monday is a free day, and tickets sell out very early. Local tour guides buy tickets and offer tours in groups of about eight people, and if you're lucky you can get in that way. According to the ticket office, tickets are first come, first served for the museum. (maybe an English/Polish translation error?) the Museum is closed on Tuesday.

Wieliczka Salt Mine tours are three hours. We did not have a reservation and were able to get tickets at 9:00 in the morning for a 9:30 English tour. Tour coaches and school children arrive in droves in the morning and we were still able to get a spot.

We arrived Auchwitz-Birkenau by car on Monday 6/3, about 1:40. We were able to get an English tour at 2:00 without a reservation. There were no reservations left to book online, so we took a chance and made the drive. The tour is 3 hours and you will not see everything in that time. Your educator will take you through some of the Blocks in Auschwitz, but not the country/race/people group memorial blocks. Rick Steves' guidebook accurately describe Birkenau as frighteningly large and it takes some time to walk to the main sites with your educator. The Birkenau "sauna" was not on the tour so our educator offered to escort us back into Birkenau after the tour (5:30) so we didn't have to go all the way back to the ticket office at Auchwitz (a 10 minute bus ride, each way) to register for the free ticket.

I’m on a bus from Zakopane to Krakow right now (stuck in bad traffic from an accident). I was able yesterday to book the Schindler factory, the Rynek Underground, and Auschwitz for this coming week and had lots of options as long as I was flexible with the time. But from what I saw, I think it’s best not to wait till the day you want to go. Fortunately, you can watch the online ticket sites and see if things are filling up, and then book accordingly.

One issue right now all over Poland is the number of school groups on field trips, which adds crowds to the major sites. That, plus the Corpus Christi holiday weekend a week ago, have kept things busy!