The Virgin Forest of Sili is part of the forest complex of Frakto at the north of the regional unit of Drama. Its rich flora includes forest trees (mainly coniferous, but also evergreen) that are also typical in Northern and Central Europe. The flora here includes various species, for example, the black pine, the fir, the beech, the Balkan pine, the European spruce, and the birch -among others. Moreover, rare wildflowers growing in the forest include the Lilium rhodopeum, the wild viola of Rhodope, the centaurea stenolepis, the fringed pink, bellflowers, rare endemic orchids, and many others.  

The forest, with its dense vegetation and rich waters, is an ideal refuge for many wild animals such as brown bears, grey wolves, red foxes, chamois, roe deer, and so on. The bird fauna includes birds such as the wood grouse,  the hazel grouse, the spotted nutcracker, the aegolius, the Eurasian eagle-owl, the coal tit, and more.

The forest has been declared a protected natural monument.