Misspent youth Helles!
Vaguely remember Stanley Street, Liverpool, in the late 60's having grids that were lifted and fruit and veg seemed to be the aroma coming from them. Yuk, not a nice smell. Never really took much notice. They seemed to be like shoots to take stuff from road level to beneath the warehouse, but that could have been a different type of grid.
These converted cellars are selling for a fortune in London again, and people walk across your ceiling. There was one shown on TV not so very long ago. Looked amazing, but the 'click clack' of the high heels was a bit off putting.