During its existence the reserve has repeatedly changed its borders and is one of the largest reserves in the Central Balkan National Park. Its area is over 3500 hectares.

 

It covers the entire upper reaches of the Cherni Osam River. The place offers the opportunity to study nature without being influenced by the human being.

 

The relief of the reserve is highly dissected and diverse.

 

In the "Haydushko igralo" and "Bivola" areas there are vertical rocks with a height of 150 meters. In the reserve can be seen rock formations with fantastic shape as well as caves, cavities in the rocks, etc. Within the boundaries of Steneto is the gorge of the same name.

 

The area has a well developed karst base, which is a prerequisite for the formation of karst caves and other karst forms.

 

The reserve is one of the long karst caves in Bulgaria - Kumanitsa, which has a length of nearly 2000 meters.

 

Here is the second deepest cave in Bulgaria - Raichova dupka, 377 meters deep.