A Sudoku game unlike anything you've played before. Fractal Sudoku takes the classic 9×9 Sudoku puzzle and nests it inside itself — three levels deep. Every cell on the top-level grid hides an entire Sudoku puzzle underneath. Each of those puzzles contains more puzzles. It's Sudoku all the way down. One game. Over 6,500 logic puzzles. One massive brain teaser. 🧩 HOW TO PLAY Start at the deepest level, where puzzles have traditional givens — pre-filled numbers just like a standard Sudoku. Solve at least 17 cells in a child puzzle to unlock its answer on the parent grid above. The center cell of each solved puzzle feeds its number upward. Work your way through the layers until you crack the root puzzle. 🎯 MULTIPLE SUDOKU VARIANTS Not just classic Sudoku — play with Thermometer Sudoku rules, Killer Sudoku (cage) constraints, and combined ThermoCage puzzles. Each variant adds new logic challenges that keep the game fresh across thousands of puzzles. ✨ FEATURES • Fractal puzzle hierarchy — 3 levels deep, 6,500+ interconnected number puzzles • Classic, Thermometer, Killer, and ThermoCage Sudoku variant rules • 5 difficulty levels from Very Easy to Extreme • Configurable difficulty bias to match your skill level • Pencil marks for tracking number candidates • Cell coloring for visual organization and strategy • Full undo support — never lose progress to a mistake • Cross-puzzle portals linking cells across different puzzles • Seeded puzzle generation — share a seed with friends to solve the same game • Achievement system to track your puzzle-solving journey • Auto-save — pick up right where you left off • Light and dark themes • Responsive design — plays great on phone, tablet, and desktop • Full touch, tap, and keyboard support 📊 5 DIFFICULTY LEVELS Whether you're new to Sudoku or a seasoned logic puzzle expert, there's a challenge for you. Choose from Very Easy, Easy, Medium, Hard, or Extreme — and fine-tune with the difficulty bias slider. 🏆 MASSIVE SCALE A single game contains over 6,500 individual Sudoku puzzles arranged in a 3-level fractal hierarchy. Minimum completion requires solving around 1,378 puzzles. Full completion: all 6,555. This isn't a quick number puzzle — it's a logic marathon.