What happened
The Reformati Franciscans settled on today's Reformacka Street in 1658, in a manor house donated by Stanisław Warszycki, castellan of Kraków. The Baroque church was consecrated in 1672, and from then on the dead were buried in its vaults – friars, but also lay benefactors, including members of the Morsztyn, Szembek and Wielopolski families. In all, about a thousand people were laid to rest in the crypts. The friars were buried without coffins, on sand, with a stone beneath the head. Thanks to the steady temperature and airflow the bodies did not decompose but mummified naturally. In the 1970s several coffins were fitted with glass lids. For years the crypts were opened to visitors only once a year, around All Souls' Day.
Witnesses
Friars of the Reformati monastery and visitors to the crypts; the vaults have been reported on by RMF FM and Radio Kraków, among others.
Explanations and hypotheses
The mummification in the Reformati crypts has a natural explanation: dry, ventilated rooms with a steady temperature dried the bodies faster than they could decay – as in other famous crypts in Europe. In recent years damp has become a problem: warm air enters through the vents, cools in the thick walls and condenses on the bodies. The friars even considered moving some of the mummies to Rakowicki Cemetery, and the crypts are not currently open to visitors on a regular basis.
Explained The phenomenon has a widely accepted, down-to-earth explanation.
Sources
More: Wikipedia (pl)