Yulen is situated at an altitude between 1600 m and 2851 m.[1] The rocks are predominantly granite and gneiss, but there are also carbonate rock. The reserve is rich in water resources and protects a number of glacial lakes, such as the Vasilashki Lakes, Tipitski Lakes, Gazeyski Lakes, Polezhanski Lakes and others which are the source of several rivers. The climate is alpine due to the high altitude. The soils are mainly brown forest and alpine meadow soils.[1]
On the territory of the Yulen Reserve there is fortress from the Antiquity. The fortress is located at about 12 km from the town of Bansko. The excavations and the archaeological finds date its foundation from before the rule of the Roman Empire. The fortress is almost 100 m in length and between 25 and 40 m wide. The only visible remains of fortification is a small section of the northern walls.