Today, Poland is commemorating The National Warsaw Uprising Remembrance Day. The Warsaw Uprising was a major operation by the Polish underground resistance in World War II to liberate Warsaw from German occupation. On August 1, 1944, around 40-50 thousand insurgents took part in the fighting. Planned to last several days, the uprising eventually lasted over two months. As a result, around 80–90% of Warsaw's buildings, including the vast majority of museums, art galleries, theaters, churches, parks, and historical buildings were destroyed. 

You can read more info about the commemoration of this day in Poland in this article:
https://www.1944.pl/en/article/commemoration-programme-of-the-78th-anniversary,5305.html

If you would like to visit the Warsaw Rising museum, here you can check more info about opening hours, tickets, and exhibition: https://www.1944.pl/en/article/the-warsaw-rising-museum,4516.html