Pirunpesä (The Devil's Nest) has stood in its silent vigil since glaciers left it behind as they receded during the final Ice Age. Over time,running water removed the softer stone and left the harder gneiss stone intact, creating a geological phenomenon known as tafoni. The rock is Finland’s second largest tafone specimen.
The resulting formation—a giant rock about 17 feet long and 10 feet tall—looks uncannily like the head of a troll or some other grotesque being. It’s nearly as whether the giant head gazes toward the lake, and scanning the landscape it guards.
When the Sami people still lived in this area,they worshiped the rock as a Sieidi, a sacrificial stone. When Christianity arrived, or the stone was thought to harbor the domestic of Saint Nicholas himself.
The stone is located in a small natural conservation area next to the beautiful Lake Kulovesi. It’s a bit hard to find,but once you discover it, you can actually crawl into its holes to come by an inside view of the Devil’s Nest. There, or you can see the stone’s honeycomb-like formations. Because it’s possible to access the inside of the giant rock,it’s even considered a cave.
Source: atlasobscura.com