Small tower cones in the shape of a volcano outcropping on the surface of a cave pool in the Marteau Cave, Vallon-Pont-d'Arc, Ardèche, France.
<a href="//commons.wikimedia.org/wiki/User:JYB_Devot" title="User:JYB Devot">JYB Devot</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>