Kolkina Dupka is the longest cave in Bulgaria with 19,164 meters of underground galleries. Until now, Duhlata in Vitosha mountain with 18,200 meters of galleries was considered the longest in the country. This is what speleologists of the "Pod Raba" caving club, which is exploring the cave, told BTA.

According to them, in addition to being the deepest and longest in Bulgaria, Kolkina Dupka is definitely also the most difficult cave to explore with many underwater rivers. Entering the cave requires special equipment and preparation.

In 2017, Kolkina Dupka, in the municipality of Svoge, became known as the deepest cave in the country with a depth of 543 m. But according to researchers, the cave has not been fully explored and there might be a new correction in the data.