The Devil's Nest
The Devil's Nest or Pirunpesä in Finnish, is an erosional cavity in Kurikka, which currently has a diameter of 14 meters and a depth of 23 meters. A staircase has been built at the bottom of the cavity and it is fenced; a small entrance fee is charged for visiting inside the fence. Access to the rest of the area is free. There is also a cafe on site.
Cave data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).