Picture students huddled around a 3D printer in a middle school classroom. They gaze at the object being printed, and exclamations of, "Where is that flag from?" "What does that symbol mean?" and "Oh; I didn't think of that!" can be heard. These examples of observation, curiosity, and critical thinking are the elusive goal of many a STEM teacher. So, how did this happen, and how can this be replicated in the classroom? The teacher and students in this scenario had just exchanged a Mystery Cube with another classroom somewhere in the world through the Global Mystery 3D Print Project. The Mystery Cube, a novel, global, 3D-printed version of a message in a bottle, helps students become engaged in developing design skills necessary for educational growth in 21st century skills while at the same time engaging in global collaboration, project-based learning, and clue-based projects. This article describes the Global Mystery 3D Print Project, and provides information on how to participate.