Velebit caves
The "Lukina jama" cave is 1431 m deep (2013), the deepest cave in Croatia, 14th deepest cave in the world and the deepest cave in southeast Europe. At its foot, there are ponds and streams including one of the largest known colonies of subterranean leeches ("Erpobdella mestrovi"), which has been ascertained to represent a new species, genus and also family. Other species discovered in the system, include the air-breathing land snails "Zospeum tholussum". Like Lukina jama, Slovacka jama, Velebita and Meduza are also located at the "Hajdučki i Rožanski kukovi" special reserve, a dedicated part of the Sjeverni Velebit national park.
Harz
Geomorphological processes have led to the formation of caves in the gypsum, dolomite and limestone layers of the Harz. These dripstone caves include Baumann's Cave, the Unicorn Cave, Hermann's Cave, the Iberg Dripstone Cave and, on the southern edge of the Harz, the Heimkehle.
Because the older formations contained many mineral deposits, they were explored very early on by the mining industry. The mines have often been turned into show mines. For example, the Samson Pit was for a long time the deepest mine in the world. Other show mines are the "Büchenberg", "Drei Kronen & Ehrt", the "Röhrigschacht" show mine, the "Lange Wand" show mine in Ilfeld and the "Rabensteiner Stollen" show mine in Netzkater.
Others have been turned into mining museums, like the Upper Harz Mining Museum in Clausthal-Zellerfeld, the Lautenthal Mining Museum with its pit railway or the Rammelsberg Mining Museum near Goslar, which is a UNESCO world heritage site. The Roter Bär Pit in St. Andreasberg also served as a training mine until the 20th century and is today, preserved true to the original, as a visitor mine.