In PRL (Polish People's Republic) times, the date was moved to 22 July to honour the day the PKWN Manifesto (a document that basically asserted communist authority over Poland) was issued in 1944. In 1989 after communism fell, the holiday was restored to its original 11 November date. To mark the occasion every year in front of the Tomb of the Unknown Soldier on Pl. Piłsudskiego in Warsaw there’s the official Changing of the Guard with all the big wigs, president, prime minister and top brass in attendance. Outside of the capital, cities all over the country hold their own parades as well.
If you're in Poland on this day you'll find that though a national bank holiday, most restaurants and bars will still be open; museums and shops on the other hand will be closed. Marking the occasion in Łódź each year is a holy mass at the Archcathedral Basilica of St. Stanisław Kostka on ul. Piotrkowska 265 (10:30), followed by a very solemn wreath laying ceremony at the symbolic Tomb of the Unknown Soldier in front of the cathedral (11:45) and subsequent military parade along ul. Piotrkowska. Things get a bit more lively as another march of historical reenactment groups and scouts carrying a 123m long Polish flag march along from ul. Piotrkowska 104 (14:00) towards Manufaktura, where a patriotic picnic is held (11:00-18:00).