Ledenika is a cave, one of 4,620 caves found in Bulgaria so far, about 16 km west of the city of Vratsa. It is 280 meters long. The temperature inside varies with the seasons. In the summer the temperature is 5C (41F). In the winter it may drop to as low as -20C (-4F). It is guessed to be around 2,000,000 years old. "Ledenika" means a huge ice box. The cave has 10 halls. The biggest one has excellent acoustics and occasionally is being used for short concerts of no more than 20 minutes duration. There are two reasons for that - the humidity in the cave is 92%, which is no good for the instruments and it is too cold for the artists. Ledenika is the most frequently visited cave in Bulgaria.