Niepokalanów monastery (so called City of the Immaculate Mother of God) is a Roman Catholic religious community in Teresin (42 km to the west from Warsaw), Poland founded in 1927 by Friar Minor Conventual Friar Maximilian Kolbe, who was later canonized as a saint-martyr of the Catholic Church.
In 1927 prince Jan Drucki-Lubecki offered fr. Maximilian Kolbe a convenient ground near Warsaw for building a new monastery, later called Niepokalanów. In autumn of the same year the first wooden barracks were built and a consecration of the new monastery took place on 7 December 1927.
The facility served as a home for the Conventual brothers, a minor seminary and a volunteer fire department. It was also a centre for charitable ministry and evangelization through the radio programmes and the distribution of printed materials. In 1930 father Kolbe founded a similar community in Nagasaki (Japan), called Mugenzai no Sono (Garden of the Immaculate).
Quick growth of the Niepokalanów required more and more space, so the area of the monastery reached 28 ha. Before the Second World War broke out, it was the largest monastery in the world, housing as many as 760 men. One of the magazines, The Knight of the Immaculate, countered religious apathy and had a press run of 750,000 copies a month. The whole publishing house used about 1600 tonnes of paper annually for about 60 million copies of papers.
During the Second World War, the monastery provided shelter for many soldiers, injured in the September Campaign and also for refugees, regardless of their nationality or religion (e. g. to approximately 1,500 Jewish refugees from western Poland). Father Maximilian Kolbe, together with four other Franciscans, was arrested by Gestapo and he died in Auschwitz concentration camp in 1941. In the end of the war (January 1945) during heavy bombardment of Niepokalanów, six friars were killed, some others injured and many of the buildings of the monastery were destroyed.