The Museum of Art in Łódź, split between two locations (ms1 on Więckowskiego Street and ms2 in Manufaktura), holds one of the finest modern and contemporary art collections in Poland. The ms1 site is the historically important one: it was founded in 1931 and assembled an international collection of avant-garde work that survived the war years against the odds.
The permanent collection runs from Constructivism, Dadaism, and Surrealism through postwar Polish art to recent contemporary work. The building itself — a 19th-century townhouse — is an odd but workable setting for the collection. If you have time for only one cultural stop in Łódź, make it ms1.