hmm. actually, not at all.. sidewalk itself, is an asphalt or brick-plated road for pedestrians. was it meant -- shadows casted by the (plain) road?.. or maybe, shadows casted by any fences, I can see across the sidewalks? in 2nd case, it makes sense for me.
?
I'm not picky! Someplace outdoors where you go for a walk and might be stepping on shadows. A dirt path or bricks, concrete or asphalt,cobblestones- your choice.
Any shadows you find... Trees, fences, people... Shadows on the sidewalk! Be creative!