This study concerns the microclimatic conditions in two historic churches of the temperate climatic zone located in Lublin, Poland: Lublin Cathedral and Post-Bridgettines Church, having regard to their underground crypts. The measurements of the air temperature and RH lasted all 2016 and were compared with optimal heritage protection values included, inter alia, in American instruction ASHRAE Handbook. Furthermore, for both buildings the historic climate was calculated, based on the European Standard EN 15757:2010, and the target ranges were specified