A plate, a membrane, eventually a whole floating alien surface — covered in thousands of loose grains. Place resonators along the rim and choose their frequencies; the surface sings, and the sand flees the vibrating regions to gather on the silent nodal lines, drawing Chladni figures in real time.
The target is a sigil, a constellation, a doorway pattern. You never draw it directly. You reason backwards from the shape you need to the vibration that causes matter to organize itself into it. Progression runs from flat plates to curved membranes, spheres, hollow shells, and finally deformable surfaces whose geometry you can also bend.
Full design notes live in puzzles/DESIGNS.md.