Video at the entrance of the <a href="https://en.wikipedia.org/wiki/Kozarnika" class="extiw" title="en:Kozarnika">Kozarnika Cave</a>, Balkan mountain, Dimovo Municipality, Bulgaria
<a href="//commons.wikimedia.org/wiki/User:Spiritia" title="User:Spiritia">Vassia Atanassova - Spiritia</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>