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.
The Chil-Mayram cave, located on the southern slope of the same massif, 2 km east of the village of Gul-Bakhar, is also a natural monument. To the west of the watershed part of the Chil-Mayram ridge, 1 km east of the village of Tash-Ata, there is the Besh-Unkyur cave. Its total length is about 250 m. Clay lamps and copper coins with Arabic inscriptions have been discovered in the cave. The local population considers it sacred and worships it.
In this same zone, there are interesting but lesser-known caves: Khatyrangly-Unkyur (the cave of chatterboxes), Kyzyl-Unkyur (the red cave) about 60 m long, Suli-Kumar (water cave), which contains a small pond, Zhen-Unkyur (earth cave) 40 m long, Biryua, Davakhan, Khatantay, Emgaklik, Teshik-Unkyur, and many other yet undiscovered or little-known caves. The zone features subsidence funnels and grottos washed by meltwater and rainwater.
In the limestone foothills and ridges of the Alay and Turkestan ranges, which exhibit signs of clay karst, there are a large number of various underground cavities. They are particularly common around the villages of Okhna, Frunze, and the rocky gorge of Kainy near Haidarkan. The caves are mysterious and impress with their extraordinary beauty. Upon returning from the underground kingdom, one particularly feels the brightness of the sun, the surrounding colors, and the gusts of strong wind filled with the scent of herbs. One involuntarily quickens their steps when a piece of blue sky is visible ahead. Proper preparation, equipment, insurance for companions, as well as psychological confidence in one's abilities and readiness for difficulties are necessary for traveling through the underground world. Porcupines inhabit the area around the caves, shedding their beautiful quills—a wonderful souvenir for tourists.
In addition to the caves, there are other sites in the zone that can be visited during excursions. The drawings on the Surot-Tash rock (painted stone) are located among the rocky ridge of Orto-Too, 5 kilometers north of the city of Osh. On the multicolored limestone slabs facing the sun, images of galloping horses, as well as images of goats, deer, and hunters are depicted. Two waist-length portraits of a man and a woman are particularly memorable. The images range in size from 20 centimeters to one meter.
The Duldul-Ata rock, with carved images of galloping horses, is located on the northeastern outskirts of the village of Aravan. It is named after the horse of Saint Ali, who, according to legend, left it here while going to battle with the white dragon that lived in the Aravan cave. The bizarre formations in the Chil-Ustun cave could have served as the prototype for the white monster. Pilgrims tie sacrificial scraps of cloth to the bushes growing around the rock. The drawings of Surot-Tash and Duldul-Ata date back to the 1st millennium BC.
On the right bank of the Arawan River, on the outskirts of the village of Aravan, the majestic fortress ramparts of the Eskiaravan settlement, belonging to the Marhamat culture (1st-4th centuries AD), have been preserved. This was once the political center of ancient Fergana—the city of Ershi. It was famous for breeding noble horses—Davani, whose images still "fly" across the rocks of the surrounding mountains. Several other ancient settlements—Debe-Korgon, Mazar-Debe—are located in the valley of the lower reaches of the Arawan River.