5) Muzeum Narodowe. National museum. Excellent collection of paintings. A big hit with my students. I can barely get them out of there.
Best museum I've been to, I spent hours in there.
No-one has mentioned Cytadel Park and the cemeteries yet, somewhere else I spent a good few hours in. If it's not your type of thing Dany, your parents might be interested.
tripadvisor.co.uk/Attraction_Review-g274847-d3176807-Reviews-Park_Cytadela-Poznan_Greater_Poland_Province_Central_Poland.html