Bats' Cave or Saint Grigorie Decapolitul's Cave is located in Costeşti commune, Vâlcea County, Oltenia, Romania. One can reach the cave departing from Bistriţa Monastery, at 630 m absolute altitude and 80 m relative altitude, on the right slope of Bistriţa Gorges.
The cave was formed due to erosion caused by Bistriţa River, has three openings, a length of 400 meters, two levels, and a negative oscillation of level of 15 meters. It has a lack of concretionary formations; presenting more openings, the cave is dynamic, ventilated all year, so the thermal amplitude is high, and the climate is humid. In specialty papers, the cave is first mentioned in 1929 by Emil Racoviţă and bio-speleological research were made in 1951 and 1955.
In Romania there are several other caves that bear the name of Bats' Cave, but this one has a religious and zoological importance. In the wall of the lower level is a small church named Ovidenia, partly built, partly carved in the rock, dating from the 17th century. It represents the secret place where were hidden in harsh times the treasures of Bistriţa Monastery and the relics of St. Grigorie Decapolitul. Under the largest opening there is the Holy Archangels church, built by monks Macarie and Daniel in 1635.
The cave is home for several species of bats. Miniopterus schreibersi lives permanently in this cave; Rhinolophus ferrumequinum, Vespertilio pipistrellus, Plecotus auritus, Barbastella barbastellus houses here during the winter; Myotis myotis and Myotis oxygnathus comes here in spring for reproduction and leaves in autumn. On the floor, under the colonies of bats, is a guano layer of 1.7 m thick, where the fauna is very rich (as the trogobiont species), the cave having a great bio-speleological importance.
Photos from here.