The museum is located in the back of the basilica. You can see in it, saber collection from the 16th to the 20th century, Hussar helmets, a large collection of robe belts, royal letters, memorabilia related to the struggle of Poles for independence. Oil paintings on sacral themes from the 17th to the 19th centuries, graphics made by Rembrandt Harmenszoon van Rijn and also those that came out of the workshop of Peter Paul Rubens.

The collection of the museum also contains manuscripts of Polish writers from the Romantic period, positivism and Young Poland, old Polish and foreign prints from the 16th to the 18th century, papal bulls, royal documents from Władysław Jagiełło to Stanisław August Poniatowski, memorabilia from Soviet gulags and Nazi camps. Engravings by European artists from the 16th to the 20th century Giovanni Vitalby, Stefano della Belli, Jan Piotr Norblin, Daniel Chodowiecki, Michał Płoński, Władysław Skoczylas, as well as drawings by Jan Matejko and Henryk Siemiradzki and watercolors by Juliusz Kossak. It is worth mentioning that the museum also has one of the largest collection of documents related to the January Uprising in Poland.