Aarnivalkea

The Aarnivalkea, in Finnish mythology, are spots where an eternal flame associated with will o' the wisps burns. They are claimed to mark the places where faerie gold is buried. They are protected by a glamour that would prevent anyone finding them by pure chance. However, if one finds a fern seed from a mythical flowering fern, the magical properties of that seed will lead the fortunate person to these treasures, in addition to providing one with a glamour of invisibility. Since in reality the fern produces no flower and reproduces via spores under the leaves, the myth specifies that it blooms only extremely rarely.

Although clearly folklore, the claim has been made that the Outokumpu coppermine — the largest coppermine in Europe at its time — was discovered due to some light phenomena or another.