3D projection on physical objects is a particular kind of Augmented Reality that augments a physical object by projecting digital content directly onto it, rather than by using a mediating device, such as a mobile phone or a head- mounted display. In this paper, we present five cases in which we have developed installations that employ 3D projection on physical objects. The installations have been developed in collaboration with external partners and have been put into use in real-life settings such as museums, exhibitions and interaction design laboratories. On the basis of these cases, we present and discuss three central design insights concerning new potentials for well-known 3D effects, dynamics between digital world and physical world, and relations between object, content and context.