One of history’s strangest and most enduring legends, the Green Children of Woolpit appeared in 12th-century England with eerie, unexplained origins. Around 1150–1200 AD, during the reign of King Stephen, villagers in Woolpit found two children, a brother and sister. They were unlike any humans ever seen.

They have skin of a striking green tint, wearing strange clothing of unfamiliar fabric, possibly metallic. They spoke no English, only a gibberish language (an unknown tongue). Refused all food except raw beans, which they ate voraciously. Claimed they came from "St.Martin's Land", a twilight place where the sun never rose, and all the people were green. They heard a loud noise (like bells) while tending their father's sheep and suddenly found themselves in Woolpit, disoriented.

Some theorize they were fairy children or from a subterranean world (linked to Celtic myths of "green fairies"). Green often represented death/otherworldliness in medieval lore. Woolpit had Flemish migrants persecuted under King Henry II. Their "foreign" language and malnutrition (causing greenish skin from anemia) might explain the story. Fungus on rye could cause hallucinations and green-tinted skin. Some UFO enthusiasts suggest they were extraterrestrials from a dimly lit planet (hence "St. Martin’s Land").

They slowly lost their green hue and learned English. The boy grew sickly and died, but the girl adapted, took the name Agnes, and later married a local man from King’s Lynn.