9×9×9 — twenty-seven sudokus, one solid
Carving a cube…
You are filling a solid 9×9×9 block of cells. Slice it flat anywhere, along any of the three directions, and what you get is an ordinary sudoku — nine rows, nine columns, nine 3×3 boxes, digits 1–9 once each.
That is 27 sudokus sharing the same cells: nine cut through X, nine through Y, nine through Z. Every digit you place lands in three of them at once, so a move that looks safe on screen can break a grid you are not looking at.
Use X Y Z to turn the block, [ and ] to step through layers, 1–9 to place, N for pencil marks, S to jump to the slice with the most you can work out right now.
Help arrives as the cubes get harder. Medium and up gets five hints. Hard and up can switch on the 3D check, which reddens a pencil mark once that digit is already taken for the cell — on this slice or any crossing one. Expert also gets Deducible, marking every cell that can be worked out this moment.
Every cube has exactly one solution and never needs a guess — a clue is only removed while the whole rest of the cube still follows by pure deduction. A digit that is not the one that belongs there turns red as soon as you place it.
That is fifteen wrong digits. The cube keeps its secrets — unless you sit through an advert.
You’ve been rickrolled
Enjoy your five extra errors
All 729 cells placed. Every one of the twenty-seven slices reads as a sudoku.