How would you spend 8 days in Poland?

No takers yet, so I'll suggest two small towns between Krakow and Warsaw: Sandomierz and Kazimierz Dolny. Both have pretty squares and views. But we didn't stay overnight so can't speak to any activities.

This pierogi making class in Krakow was a highlight for many of us on the Best of Poland tour itinerary last year: https://krakowurbantours.com/tours/home-cooked-krakow/

I'd recommend heading south from Kraków towards the Tatra mountains for your outdoor activities. It's beautiful down there and you won't find a town with 50k+ people either. Its not the easiest by train unless you have a lot of time. But its a part of Poland where most of the tourists are other Poles, and you won't see many English menus or speakers in the service industry. Zakopane is the main hub, is a little tacky, but has everything you need. The architecture in the south is also very fascinating.

Well, 2 months since the original posting for this thread, here’s a possibility for anyone who comes across this - Augustów. It’s in the far northeast section of Poland, surrounded by lakes (ideal for kayaking), and flat (bicycling paradise). We’ve been in Poland for 2 weeks, and have more than 2 to go, and had considered Augustów for just those reasons, having read recommendations in the Lonely Planet guidebook. Unfortunately, it’s been chilly and windy so far, with occasional rain, so it seems just a bit too early in the season. Were going to other places instead, and might or might not get in a bike ride elsewhere, but Augustów will have to wait for a future trip for us.

July/August would be much better for the OP, and while it’s apparently a popular location for Poles to visit, not too far from Warsaw, there aren’t many visitors from other countries.