Caucasian Biosphere Reserve
This natural reserve has the second-largest protected area in Europe and the largest one in Caucasus mountains of Russia. It occupies the mountain ridges of Krasnodar Krai, Adygea and Karachay-Cherkessia, including part of Greater Sochi metropolitan area (Khosta district and Krasnaya Polyana), bordering Sochi National Park.
Caucasian Biosphere Reserve is the richest biodiversity treasury, having no equivalents in Russia and an international value as a piece of untouched nature with primeval habitats. Reasonably, this unique area is included into the UNESCO World Heritage List. The official site of the reserve is available in Russian only: 
Flora and fauna
Two exclaved parts of the reserve, those are located inside Greater Sochi, are easy to visit: yew & boxtree wood at Khosta and the wild animals nursery at Krasnaya Polyana.
To visit other parts of the reserve, you need to get special permit, requiring the following:
In Sochi you can get the permit at the reserve's headquarter: Karl Marx street, 8, room 10, Adler district, Sochi.