A great experience if you are, like us, a normal citizen, having seen bats occasionally during your south European holidays. This place is the pure concentration of everything you know about bats. A German research group counted the bats (with modern technology) and the result was an amazing 100 million creatures... and rising!
Every day at about 6pm they come out of their cave.  Imagine a constant bats stream for about 3 hours!! In the beginning it  is a rather thin line, looking like a bunch of moskitos  far away. After  about 10 minutes they start flying directly over you and the already  darker evening sky starts to move in all shades. Pretty cool! 
Every Saturady visitors are allowed to actually enter  the cave at 6pm. For sure this must be even more an intense moment of  pure nature at its flow.