The biosphere reserve "Steneto" is located in the Troyan mountain, in the upper stream of the Cherni Osam river. It was proclaimed as a natural reserve on April 5 1979 and was established to preserve the nature in the majestic gorge "Steneto" and is included in UNESCO’s "Man and Biosphere" programme.

"Steneto" is a home of the greatest variety of forest and rock birds on the Balkans. It is also the area most densely inhabited by brown bears in Bulgaria, and Bulgaria has been acknowledged as one of the most important bear areas in Europe.

The Karst region of the reserve is strewn with many caves, including Kumanitza - one of the longest water caves in Bulgaria (1656 m) and Raychova dupka (377m) - the deepest cave in Bulgaria.