In the 1780s the honorary member of St. Petersburg Academy of Sciences, natural scientist Eric (Kirill) Laksman became interested in the Baikal area caves, which are created in karst rocks. He had probably collected the first scientific data on the enigmatic and many-sided world in the very center of Eurasia. Here is what he wrote about the Nizhneudinskaya cave, well-known today: "It took me 24 hours to measure and describe it, to gather stalactites, the enormous resources which nature had hidden in the remote, most terrible and surprising country." Today two hundred similar objects are well known, many of which are mapped, in some of them tourist itineraries are paved, while experts know incomparably more about the origin and development of different underground caves of Irkutsk amphitheater, as the southeastern part of Irkutsk-Cheremkhovsk piedmont plane is called, which is surrounded by the stepped bottoms of Eastern Sayan Mountains, Maritime and Baikal crests from the south-west, south and south-east. In the journal Priroda (Nature), No. 5, 2007, Yelena Trofimova, Cand. Sc. (Geography), told about the modern state of these caves. The western coast of Baikal, the lower flow of the river Kitoya and the Uda basin - these are the places where speleologists set forth to descend into underground systems. The entrance can be located both at the top of an inaccessible rock and at waterline, while its dimensions vary from 0.3 - 0.5 m to 15 - 7 m. Though these caves are weakly watered, in some of them one can see "bottomless" lakes with siphons. In 50 percent of the examined area there are carbonate, sulphate and salt-bearing rocks, "threaded" with seismogenic cracks and exposed to intense physical weathering. Underground labyrinths are formed in them. Here karst processes are developed at a high rate - from 50 mm/1,000 years showing themselves even at a depth of 1 kilometer. Absolute altitudes on plains are 250 - 500, while in mountains - 1,000 - 2 ... Read more