This ornate Gothic doorway dating to the fifteenth century is apparently a popular spot for wedding proposals. Folklore has it that the doorway once had a very unusual use: Lepers would stand at one side of the doorway and whisper their sins into the half pipe in the architrave. The priest would stand at the other side of the arch, far enough away to avoid infection, listening to the confession emerging from the architrave.
Like all whispering arches, sound skims around the inside of the curve because of the geometry – see below for a simple model of sound as a snooker ball bouncing around a circular table. Being a half-pipe probably helps keep the sound close the arch.