The catacombs in the crypt under the Reformed Franciscan church are among some of the most secret places in the city of Kraków. Unique climatic conditions found in the basement caused the bodies of the dead to undergo a process of natural mummification whereby they remain in an excellent state of preservation. Among them, hidden away since 1667, are the remains of many monks and members of Polish noble families. Monastic books reveal that in total almost 1,000 bodies were placed in the catacombs over the years, among them around 730 lay people and 250 monks. The crypts, now holding only about a hundred bodies, are now made available for public viewing just once or twice a year, traditionally on All Souls' Day (November 2nd), the day after All Saints' Day. In the past, the mummies attracted crowds of visitors, causing adverse climatic challenges.