That’s a neat hack! Keep the cardboard shape but add a cheap fisheye lens to widen the field of view, and use a small LED strip around the edges for ambient light. Mount the projector on a tripod or a DIY arm so it can swivel with a servo—then wire a simple gyroscope to the headset so the image shifts as you move. For the backyard, paint a subtle gradient on a flat wall or screen the ground with a light‑absorbing tarp and project a night‑sky or a virtual canopy. A few motion‑sensing IR LEDs will let you “walk” through the scene, and you can layer audio from your phone to match the visuals. It’ll feel like stepping into a backyard‑grown VR playground!