Prototyping in 3D isn't the same as in just two dimensions. Compared to regular, flat websites, augmented and virtual reality have very different requirements when it comes to creating prototypes. To close a gap in the medium-fidelity range of AR/VR prototyping methods, we've created 360theater, which makes use of dioramas and 360° content for creating physical-digital prototypes. We've used our new method in workshops with design students and found that it comes close to the final experience while complementing other methods with different levels of fidelity.