There are rare instances of contour drawings of famous architectural structures and monuments with a variety of parts made in a realistic manner. Such coloring is complex to implement and is designed for adults.
Today there is a large set of coloring books. You can find coloring-cursive books, books outliners, for boys (all sorts of appliances, machines, robots, etc.), for girls (fairy-tale characters, dolls, funny funny little animals). There's even a wallpaper coloring books that opens a wide field to have enough space for young artist.