Osówka (Germ. Säuferhöhen), is one of the elements of the unfinished Nazi military complex called “Riese”. The total length of corridors of Osówka complex is about 1,700 m and its capacity amounts to 30,000 m3. As described geologically, Osówka is situated within the Sowie Mts. Massif which consists mostly of various gneisses with different structural characteristics, but with a constant mineral composition. The rock-forming minerals are feldspar (oligoclase), quartz, biotite and light micas, accesory minerals are garnet, sillimanite and dysten. Fine-grained shallow-sea deposits were probably a protolith of these rocks. The study aimed at first mycological evaluation of the air and the rocks in Osówka adit. The air samples were taken from one location outside the adit and from four locations inside of it. Mycological evaluation of the rocks inside the adit was performed using three different methods. Fifteen taxa of filamentous fungi were isolated from the internal air sampled, and several taxa - from the outside of the adit, whereas only eleven species were isolated from the rocks. Cladosporium spp. were the fungi most frequently isolated from internal atmosphere of the underground Osówka complex, and from the external air. On the other hand, the fungi most frequently isolated from the rocks were Aspergillus niger group (when using swab sampling procedure) and Mucor spp. (from debris and rinse sampling procedure).