The Postoina cave is located in the Republic of Slovenia, 54 km southwest of the capital Ljubljana, the second largest cave in Europe. The cave is 27 km long, 115 meters deep and 562 meters above sea level. It is formed by the long-term dissolution of the Beaverka River's submersible flow to the limestone formation. You need to take a special small train to enter the underground world, the cave has a stalactite hall that can accommodate tens of thousands of people, can hold symphony performances and concerts, and there is also the world's unique Slovenian doll fish (proteus), which is an eye-opener.