https://www.openstreetmap.org/way/1171448731

what kind of surface is there?

Flat-machined stone ( https://wiki.openstreetmap.org/wiki/Tag:surface%3Dpaving_stones ) ?

Is it cut stone but not entirely flat and not entirely covering surface? ( https://wiki.openstreetmap.org/wiki/Tag:surface%3Dsett )

Stone pieces, not flattened at all ? ( https://wiki.openstreetmap.org/wiki/Tag:surface%3Dunhewn_cobblestone )