Description: In many walled medieval cities, there is a street just inside the walls that likewise continuously encircles the rest of the city. Morbis Street serves that function in a particular High Fantasy medieval-style walled city. Most of the year it’s perfectly normal.
One night a year, however (the exact date doesn’t matter, as long as it’s the same date every year), anyone who ‘Walks Up Morbis Street’ while carrying a certain arcane symbol vanishes, never to return. And if somebody does walk the Street on that night and vanishes, then somebody else (carrying the same arcane symbol) will appear, too. A person for a person. Most people who arrive do so with at most a traveler’s pack, but at least one person has arrived pushing a handcart.