The Biserna Cave near Shumen, which has been closed for almost 40 years, is now accessible to tourists. The natural landmark can be seen twice a year - in spring and autumn, for about two months.
The restrictions are because of the bat colonies that inhabit the cave.
The cave is called "Pearls" because the water droplets on the formations shine like pearls.
The artistic illumination gives different glare to the beautiful karst forms. The cave is 3,500,000 years old, 2,700 meters long and has two levels - at the bottom is the river, and in the upper gallery are the strange natural forms.
Biserna was discovered in 1928 by the French geographer Jean-Denis Barbier du Bocage and is located 404 meters above sea level in Shoumen, with a temperature of 11 degrees and humidity 100%.
