Orlova Chuka

Orlova Chuka (Bulgarian: Орлова чука) is a cave situated in the Danubian Plain, north-eastern Bulgaria. With a total length of 13,437 m, Orlova Chuka is the second longest cave in the country after Duhlata. The cave was discovered in 1941 and opened for tourists in 1957. Orlova Chuka is home to 14 species of bats.

Source: Wikipedia (CC BY-SA 4.0) — https://en.wikipedia.org/wiki/Orlova_Chuka