Devetashka Cave, Devetaki, Bulgaria

© Jasmine_K/Shutterstoc

The skylights are a nice touch. Devetashka Cave, Devetaki, Bulgaria

Step into the depths of Devetashka Cave and journey through time in one of Bulgaria's many natural wonders. However, there is one condition for this adventure: you must not be afraid of bats! About 30,000 of these flying mammals call the cave home. The karst cave, which was formed by the dissolution of carbonate rocks by water, is now part of a public park. The presence of humans in Devetashka Cave is thought to date back to the Early Stone Age, around 70,000 years BCE, and Neolithic artifacts from 6,000-4,000 BCE have been found here. Several large openings in the cave cast natural light into the chambers, offering better illumination for photographers and nature lovers alike.