Ledenika is a cave in the Northwestern parts of the Balkan Mountains, 16 km away from the Bulgarian city of Vratsa. Its entrance is approximately 830 m above sea level. The cave features an abundance of galleries and impressive karst formations including stalactites and stalagmites. It was first discovered around the beginning of the 20th century and has been open to tourists since 1961. (source: Wikipedia)
The Concert Hall chamber has an enormous variation of stalactites and stalagmites. The chamber sometimes hosts live performances as it has superb acoustic properties hence the name of the chamber.