This experiment uses the boundary of a regular 4D five-cell. Each of its five boundary cells is a 3D tetrahedral volume. Float inside those volumes and cross broad openings in their actual shared triangular faces. The whole-shape view is a projection for inspection; overlapping projected surfaces do not create shortcuts.
Five shared-face passages form a permanently open loop. The other five have shutters driven by the position of their face centers along the rotated W axis. The visible openings and camera crossing use the same aperture. Rotation changes access, not which cells share a face. An opening can widen but cannot close while you are crossing it.
The camera preserves its view through a crossing. Position, gaze, screen up and movement all follow the same reciprocal seam transform used by the view through the opening. The next room’s floor may be tilted; the camera never snaps to that room’s vertical. Turning adds no roll, and E/Q follows your carried up direction. Reset camera starts a fresh local frame. Neighbor views extend two crossings deep, so distant views are still limited. This is a free-camera geometry experiment, with corridor, boundary and opening checks, not a moth physics controller or finished movement course.
All five regions now have enclosed routes with camera collision. B–E have central junctions and connecting passages. Corridors and triangular rims have softened corners. A contains an ordinary 3D corridor loop, an upper branch to D and a lower branch to C. The shells and camera clearance use one continuous rounded field; the route buttons aim toward the next bend and never teleport. The 90° and 180° presets expose the two continuations. Lighting, one-unit tile markings, floors, walls and roofs are temporary geometry aids, not a change to the accepted open-sky art direction. Nearby corridors stay rigid: rotation changes which shared-face openings are usable, rather than physically swinging the same hallway overhead.
A is the start and the rose marker inside D marks the approach to the shark. The boss arena remains a separate ordinary 3D setting. No water, scenery, combat or campaign integration is included.