During the war, Ringelblum and his family were resettled to the Warsaw Ghetto. There he led a secret operation code-named Oyneg Shabbos (Yiddish for "Sabbath delight"). The activities of the group were kept so secretive that not even the inhabitants of the ghetto were aware of the operation. He spent his days collecting information, and wrote notes at night. Together with numerous other Jewish writers, scientists and ordinary people, Ringelblum collected diaries, documents, commissioned papers, and preserved the posters and decrees that comprised the memory of the doomed community. Among approximately 25,000 sheets preserved there are also detailed descriptions of destruction of ghettos in other parts of occupied Poland, the Treblinka extermination camp, Chełmno extermination camp and a number of reports made by scientists conducting research on the effects of famine in the ghettos. The operation used the Jewish Social Self-Help (ZSS), an organization tolerated by the Nazi Party, as a cover for its activities. The office of this social service is now the storage site of the archives.