“ Another real world thing. White tea. Can only be picked two days a year, the two days before the flowers blossom. Could be a similiar plant that...is the deadliest poison known, cure known diseases or psychosis, or a potent herb that just tastes awesome.”
“ A planet (or city, valley ect) where those who enter witness protection can escape old age and death itself, so they can live for centuries without aging-provided they maintain their cover perfectly. If they are outed by anyone or ever utter their true name, they age the number of years they have not aged since the day they entered witness protection (which might mean that they age centuries in seconds and crumble into dust and bone.)”
“ A village where everyone goes blind sometime during puberty. What could be causing this? Perhaps something in their diet. Or some malignant gene. How would an entire village where only young childen can see function?”