The real sky and the Earth beneath you, through any surface of the room. Floor and ceiling start as portals; point at a surface and select to toggle it. Face north (phone compass) and squeeze to calibrate. A/X opens the control panel (every option, aim and select), B/Y cycles the Earth style, the thumbstick scrubs time.
Preview: drag to look, double-click toggles the surface at the centre, m opens the panel (click its buttons). n north e/E Earth style s sky [ ] ±1 h { } ±1 day 0 now.
Stars: d3-celestial (HIP, mag ≤ 6). Coastlines, land: Natural Earth. Ephemeris: astronomy-engine.