The Devil's Nest

The area's bedrock consists of coarse-grained reddish granite containing feldspar crystals with a diameter of 2–4 centimeters.

To the west, northwest and north of Pirunpesä is a large deep rock area consisting mostly of granodiorite and quartz.

[3] In the summer of 1980, business representative Pekka Kunnas and Jalasjärvi municipality's director of schools Kustaa Ala-Hautala were told about a special, rather round rock depression located on Ylivalli's Isovuori, which was filled with large boulders.

The municipality of Jalasjärvi decided to empty the depression, as Pirunpesä was a touristic and geologically interesting destination.

[3] At the beginning of 1997, the Yylivalli village committee started deepening Pirunpesä again, on the initiative of amateur scientist, writer and pseudoscientist from Turku, Keijo Parkkusen, thus reaching its current depth.