Three real beams, arranged so that from one exact viewpoint they appear to close into a loop that cannot exist. Watch it break apart and reform as the camera drifts, or drag to look around freely. The trick relies on an orthographic camera looking exactly along the (1,1,1) diagonal: any displacement of geometry along that axis is fully invisible in screen space, so the open end of the staircase silently lands back on its starting point. Use the slider below to nudge the viewpoint away from that magic angle and watch the illusion collapse into the true open spiral.