Krubera Cave
The difference in elevation of the cave's entrance and its deepest explored point is . It became the deepest-known cave in the world in 2001 when the expedition of the Ukrainian Speleological Association reached a depth of which exceeded the depth of the previous deepest-known cave, Lamprechtsofen, in the Austrian Alps, by . In 2004, for the first time in the history of speleology, the Ukrainian Speleological Association expedition reached a depth greater than , and explored the cave to . Ukrainian diver Gennadiy Samokhin extended the cave by diving in the terminal sump to 46 metres' depth in 2007 and then to 52 m in 2012, setting successive world records of 2,191 m and 2,197 m, respectively. Krubera is one of the two known caves on Earth deeper than 2,000 metres.
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.