Transparent Watch Cases

Watches with the entire case (the front, back and sides of the watch case) made from a transparent material. The rarest, and best option is scratch resistant sapphire crystal, where you need something as hard as a diamond or sapphire to scratch the case. Usually these types of cases have a skeletonized movement inside so you can observe the watch at work, and sometimes there is a thin steel outer shroud placed around the case to provide a connection to the straps.