Expo Yama Crass is the largest museum in the world dedicated to presenting the history of the formation of the karst cave and the nature of Postojna and its history in a modern and exciting interactive way for adults and children alike, in addition to it includes exhibitions related to the characteristics of individual geological periods, continental drifts, the origin of life and the emergence of humanity from the formation of the earth to the present day It also provides a dedicated section with more than 3,000 butterflies from all over the world.