Kolkina Dupka

Kolkina Dupka is a large vertical, water-active cave in the Ponor Mountains (Western Stara Planina), above the village of Zimevitsa in Svoge Municipality. Its entrance lies at about 1,295 m a.s.l., and the system runs through karst terrain shaped by underground rivers, waterfalls and long galleries. As of 1 January 2026, 25,921 m of passages and 562 m of depth have been surveyed, making it Bulgaria’s longest and deepest cave. Exploration began in 1963 and continues today as teams map new branches. Because of shafts and wet sections, entry requires full rope technique and solid speleological experience.