The Chil-Ustun Zone includes the Chil-Ustun, Chil-Mayram, and Keklik-Too mountains located around the village of Aravan, which rise sharply among the flat plains with rocky ridges along the Arawan-Say River valley. The distance from the city of Osh is about 30 km along the highway west to the village of Aravan.
The territory of the zone is situated within the arid landscapes of Southern Pritfergan, occupying the hilly slopes of low ridges. In small areas that have remained in their natural state, rocky ephemeral-sagebrush semi-deserts prevail. The same sparse vegetation covers the relatively low mountain ranges of Chil-Mayram and Chil-Ustun. They are surrounded by vast scorched spaces, over which hot air flows. On the northern-facing slopes, almond and pistachio trees grow.
The main attractions of the zone are hidden deep underground in numerous karst cavities that cut through the rocky massifs. The most remarkable of all is the Chil-Ustun cave ("forty columns"), located 4 km from the village of Aravan on the southeastern slope of the Chil-Ustun massif. It stands out among others with its incomparable beauty of the underground kingdom. The cave has a complex cavity structure along its entire length (about 370 m). It consists of six fairly spacious halls connected in some places by narrow and winding passages, known as "changing rooms." The "gothic" vaults of the halls are supported by numerous sparkling light-pink columns, which appear to be a magnificent creation of a most talented architect. Unique lace-like "chandeliers" hang from the ceiling, and carved "sconces" made of multicolored crystals are frozen on the walls. The crystals are not silent; a gentle touch produces delicate musical sounds, distinguished by their pure tone. In this cave, the winged expression "architecture is frozen music" takes on a material form.
In the first hall of the cave, numerous ancient images and inscriptions in various languages can be found on the walls and vaults. The Chil-Ustun cave is a natural monument, an archaeological site, and a geological reserve. Approaches to the cave follow a heavily sparse chain of ledges and crevices that stretch along the limestone wall of the Chil-Ustun mountain massif.
At the western end of the Chil-Ustun ridge, near the village of Sasyk-Unkyur, there is another cave declared a natural monument and archaeological site. The Sasyk-Unkyur cave is a huge grotto about 40 m long, 13 m wide, and 15 m high. Stone tools have been found here. Several species of bats inhabit this cave.
