Spanning a territory of 3671 ha or 36.71 km2, it was declared in April 1986 to protect primary ecosystems of coniferous and mixed coniferous–deciduous forests.

[1][2] It is a strict nature reserve (1st category protected territory according to Bulgarian legislation and IUCN classification).

One of the most visited parts is the meadow of Kirilova Polyana, overlooked by forests and the raising summits of Kupenite (2,731 m), Lovnitsa (2,695 m), Zlia Zab (2,678 m), Dvuglav (2,605 m), Orlovets (2,686 m) and Eleni Vrah (2,654 m).

The high-mountain population of the highly localised endemic Rila oak (Quercus protoroburoides) is unique for the country, and in places it forms the upper forest boundary.

[2][3] The fauna is diverse for the reserve’s limited territory, with a number of rare mammal and bird species of conservation importance, including brown bear, gray wolf, red fox, chamois, red deer, roe deer, wild boar, common buzzard, boreal owl, western capercaillie, hazel grouse, black woodpecker, northern nutcracker, European robin, Eurasian crag martin, etc.