The present-day mountain relief in Central Balkan National Park is the product of mighty geological processes, refined over millennia by water and wind. Rounded ridges and high peaks alternate with deep canyons, vertical rock faces and caves. The Balkan Range is the central structural mountain strip in the Balkan Peninsula. It is made up of several basic types of rock, most commonly southern Bulgarian granites, sandstone, crystalline schists, etc. At altitudes over 1,800 meters above sea level there is some evidence of glacier activity in the geological past.
Mountain cliffs and rocky landscapes occupy about 2,000 hectares (3% of the entire Park territory). Among the more original natural formations are Skalniya Most (the Rock Bridge), Markovata Dupka (Mark’s Hile) and the spindly vertical Kalchovi Kamani stone pillars. In the Park is located the unique Djendemite (literally: the Hells) rock complex combining centuries-old forests, vertical rock faces, and a mighty strip of exposed rock, that is one of a kind in Bulgaria. Another unique formation is the system of gorges and canyons that comprises the narrow valley of the river Stara Reka, the canyon of the Cherni Osam river, the valleys of the rivers Sokolna and Byala.
Though karst bedrock accounts for a relatively small part of the protected area, it is the scene of many deep caves and precipices. Remarkable for its bottomless caves is Steneto Reserve, where Raichova Dupka, the deepest precipice cave in Bulgarian (377 m. in depth, 3,333 m. combined length of all galleries) is located; also here is Kumanitsa, the longest flooded cave in Central Balkan (1,656 m. explored length, average outflow of the underground river 600 liters per second).
The caves and canyons, the rock faces and cliffs are inhabited by six species of bats endangered on a world scale, by a number of petrophilic birds, and by various rare and beautiful plants.