No person shall, without the consent of Council, build any cellar door, window way, coal hole or other opening of any kind into or through any sidewalk or footwalk; and where any such way, hole or opening exists in any sidewalk or footway with the consent of Council such opening shall never, under any circumstances, be left open so that pedestrians might fall therein, nor shall it at any time be opened if there is danger of pedestrians falling therein, unless someone is stationed to warn pedestrians of the danger during the time such aperture is open.