The medieval wall below the Mealhouse is disappearing behind a new structure.
No doubt I will be corrected, but I think there has long been debate as to whether the wall was merely a retaining wall to support the hill upon which the Market sits, or the base of a defensive wall round a bailey attached to a 'motte' keep on Castle Yard.
Either way, you will have to hurry to see it before it is obscureded by a new building, like much of Stockport's medieval history.