Deep below the surface of Romania’s Constanta County lies Movile Cave, which remained cut off from the outside world for 5.5 million years. After Soviet workers stumbled upon it in 1986, researchers discovered a whole new ecosystem of organisms living inside the cave, feeding on methane and carbon dioxide from flowing geothermal waters. Of the 48 species identified, 33 were new additions to the planet. Because of the poisonous gasses and the precariousness of the cave itself, Romanian authorities have only let about 100 people inside it since its discovery. To learn more about Movile Cave, watch the video below. View photos of the creatures by Patrick Landmann and Thierry Berrod underneath the video.