The will'o'wisp, is a unique phenomenon described as a flickering light floating or dancing hovering above a bog or marsh, continually out of reach. It straddles the worlds of folklore and science, mentioned worldwide, from the moors in Scotland throughout Asia and Africa. A will'o'wisp' reputation varies from the impish to ghoulish, depending on the culture and location. Some cultures describe then as spirits leading travelers astray, witches or simply as lost souls. However, its consistent appearance through the centuries lends credence to it being a real, if poorly exclaimed phenomenon.
Scientists have surmised that its phosphorescence is due to marsh gases oxidizing (phosphine, diphosphine, and methane) or the luminescence of phosphine under perfect conditions, excited, but not aflame.
Its recent cultural resurgence appearance is from the Disney movie Brave. Are they real? I don't know, but sometimes a good mystery deserves to remain unsolved.
More info on Wikipedia here:
https://en.wikipedia.org/wiki/Will-o%27-the-wisp