https://www.degruyter.com/document/doi/10.1515/opar-2022-0328/html
https://nyadagbladet.se/kultur/overnaturlig-grotta-i-finland-undersoks-av-forskare/attachment/pirunkirkko-finland-grotta/
https://www.degruyter.com/document/doi/10.1515/opar-2022-0328/html