I definitely recommend visiting Gniezno and the Museum of the Origins of the Polish State
(Muzeum Początków Państwa Polskiego w Gnieźnie)
Much of the museum has English texts as well as Polish.
There's a lot of information there. I visited last year, but at that time I did not know I was a descendant of the Piast family. The sculpture of Bolesław Chrobry is impressing with its detail, where he is holding an Ulfbehrt sword.
Also Doubravka is supposed to have been buried there in the cathedral.
