The STENETO Biospheric Reserve is famous for the most virgin and intact forests in Bulgaria. The majestic canyon of the Kumanitsa River is included in the reserve borders. Just before the Big Waterfall the river disappears underground to show up again a kilometer further down the canyon, at the cave, where the Cherni Osum River rises. Both slopes of these rivers are exceedingly steep and very difficult to access, and in their lowest points they turn to vertical 160-170-meter-tall walls, forming their canyon. About 80% of the forests are beech forests, over 200 years old, and some groups reach the age of 320. Steneto is among the richest cave regions. In the Chaushov Dol area there are several caves: Malkata Yama (The Little Pit) – an abyss cave with a depth of 232 meters, Borova Dupka (Pine Hole) – 156 meters deep, as well as the deepest Bulgarian cave – Raichova Dupka (Raicho's Hole) – 372 meters deep. Not far away is another abyss cave – Ptichata Dupka (Bird's Hole), with its unique vertical line that separates it in two parts, one division leading to a large hall full of incredibly beautiful cave formations, and the other division ending in another hall with steps and lakes. Steneto has preserved an exceptionally rich world of animals, like bears, wolves, wild goats, deer, does, pigs and many others, as well as a lot of birds' species. To pass across Steneto you can use the path going along its western slope, or the river bed.