The caves of Grottedal, Kronprins Christian Land, northeast Greenland were examined for microbial activity during the 2019 Northeast Greenland Caves Project. Given the freezing temperatures, desiccating conditions, and poor organic content of these caves, little microbial activity was expected. Nonetheless, field observation demonstrated a surprising level of microbial activity, dominated by photosynthetic species in near-entrance zones. This included the presence of extremophilic green algae (chlorophytes), along with cyanobacteria that formed photokarren. Other microbial activity that was observed indirectly included microbialites and iron-oxide deposits, which might indicate microbial contributions to speleogenesis when the region was warmer and cave development was ongoing. The Grottedal area and caves have several environmental features in common with Mars: a polar desert under desiccating, low-light conditions. Nonetheless, observations at Grottedal indicate that significant microbial activity, which can generate long-term geochemical and geomorphological signatures, is possible. Such data suggest that the Grottedal caves could provide an important testbed for future astrobiological investigations and instrument development.