Devil's Church Cave, or Pirunkirkko in the local language, found in eastern Finland, has been the site of rituals and magical practices by shamans and faith healers for centuries, but the supposed mystical properties of the cave may be attributed to its unique acoustics.
A pair of researchers, Riitta Rainio and Elina Hytönen-Ng, have been studying the cave and discovered that the shape of the cave's back wall may be responsible for the supernatural beliefs associated with it. They started their research by observing a shaman performing a healing ritual which often used drums and a cacophony of sounds including screams, yells, shouts, stomps, and loud bangs.
The mix of sounds are then amplified by the wall of the cave producing a "distinct resonance phenomenon" which were more pronounced at a frequency of 231 Hz. They write that this resonance may have been what shamans and people of the past deemed to be a supernatural presence or exceptional energy that helped them connect with nature and one's own roots.
(Image credit: Trip Advisor)