Step through time and into the cavernous depths of Devetashka Cave in Bulgaria, a sprawling prehistoric complex which humans called home for tens of thousands of years. These days, it is home to bats, about 30,000 of them, as well as rare birds and reptiles. This karst cave was formed by erosion and is now part of a public park. Humans are thought to have sought shelter here as far back as the Early Stone Age, about 70,000 years ago, and many Neolithic artefacts from 6000-4000 BCE have been discovered. Several large openings in the cave cast natural light into the chambers, offering better illumination for photographers and nature lovers alike.