The "Temnata Dupka" cave is the longest cave in the Balkan Mountains (5,300 m). Its entrance is located in the rock ridge of the Lakatnik (Milanovo) Rocks, roughly 27 meters above the Iskar River, within the territory of Milanovo village, northwest of Lakatnik railway station.
Formed in dark Middle Triassic limestones (Ladinian) of the Milanovo syncline, it consists of a system of two main galleries with adjacent branches. The northeastern section is the longer one, extending about 800 meters along the main axis, while the main underground river flows along it.
The underground river usually discharges through the "Zhitolub" karst spring, but during extreme rainfall and snowmelt, its level rises and the water flows out through the cave's entrance. The cave fauna is highly diverse, with 18 identified species of troglobites adapted to a life of complete darkness. Remarkably, Bulgaria is among the nations with the highest diversity of cave organisms.
Known as the ultimate "school" for Bulgarian cavers, "Temnata Dupka" has played a vital role in the history and development of Bulgarian speleology.
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