Play Nurikabe — Free
The classic island-and-sea logic puzzle from Nikoli. Shade cells to flood the grid with sea and leave numbered white islands — each island exactly as big as its clue, no two islands touching, the sea all connected, and never a 2×2 patch of water. Hand-crafted 5×5, 7×7 and 9×9 boards, each with a verified solution.
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What is Nurikabe?
Nurikabe is a Japanese logic puzzle in which you paint a grid into two things at once: a spreading body of water called the "sea", and a scattering of dry "islands" that poke up out of it. You are given a square grid with a handful of numbered cells already in place, and your only tool is shading. Every cell you shade becomes sea; every cell you leave white becomes part of an island. When the picture is finished, each island has to hold exactly one of those printed numbers, and the number tells you precisely how many cells that island is made of — a clue of 3 marks an island of three white cells, a clue of 1 marks a lone white cell surrounded by water. The whole delight of the puzzle is that the answer is not written anywhere; it is a shape you have to reason your way into, one forced cell at a time.
The puzzle was popularised by Nikoli, the Japanese publisher famous for turning Sudoku into a worldwide craze, and it first ran in their magazines in the early 1990s. Its name is borrowed from the nurikabe, a creature of Japanese folklore imagined as an invisible wall that rears up in front of night-time travellers and refuses to let them pass — a fitting image for a rising wall of water that boxes in every little island. That island-and-sea theme is what gives Nurikabe its unusual character among grid logic puzzles: you are not filling in numbers or drawing a single line, you are carving a coastline, and four simple rules about land and water pull against each other until only one map can possibly be correct. Every board on vygam is hand-authored and its solution machine-verified against all four rules, so there is always a clean path of deduction and never a need to guess.
How to Play Nurikabe
Nurikabe has exactly four rules, and the board is only solved when all of them are true everywhere at the same time:
- One number per island, sized to match. Every island — an orthogonally-connected group of white cells — must contain exactly one number, and that number must equal the total number of cells in the island. No island may be numberless, and none may hold two numbers.
- Islands never touch. Two separate islands may not sit edge to edge horizontally or vertically. They are allowed to meet only at a diagonal corner, so there must always be at least one sea cell between any two islands.
- The sea is one connected region. All the shaded water cells must join together into a single group linked through shared edges — no lake of sea may be walled off on its own.
- No 2×2 of sea. The water may never fill a two-by-two square completely. Every block of four cells in a square must include at least one white island cell, which keeps the sea flowing in thin, winding channels.
These four rules are the entire game, and the fun is in how tightly they interlock. The size rule tells you how much land each clue needs; the no-touch rule forces sea into the gaps between islands; the connectivity rule stops you walling the water off; and the no-2×2 rule keeps the sea from pooling into fat blocks. Push on any one of them and the other three push back, and it is exactly in those collisions that the next certain cell reveals itself.
Nurikabe Tips & Strategy
Nurikabe looks intimidating on a big 9×9 grid, but almost every board comes apart through the same handful of repeatable ideas. Learn to see these patterns and you will find yourself marking forced sea and forced land without ever guessing — which is how the puzzle is meant to be solved.
Walls between clues are always sea
Because two islands can never touch, any cell that sits directly between two different numbered cells — orthogonally adjacent to both, or on the single square that would join their regions — must be sea. The very first thing to do on a new board is scan for numbers a knight's-move or two apart and shade the cells that would otherwise let their islands merge. A clue of 1 is the strongest of all: an island of size one is complete the moment you place it, so every cell orthogonally around a "1" is guaranteed sea. Painting those in immediately usually cracks open the rest of the grid.
Grow each island only where it can fit
An island must reach its exact size, no more and no less, so treat each clue as a budget of white cells that has to spread out from the number without ever touching another island. When a clue can only extend in one direction — because sea, the grid edge, or a neighbouring island blocks the others — that extension is forced, and you can confidently leave those cells white. Conversely, once an island already has as many white cells as its number, every remaining cell around its border must be sea, because adding one more would overfill it. Counting the reach of each number is the engine of most Nurikabe deductions.
Never let the sea drown in a 2×2
The no-2×2 rule is a constant safety check and often a source of forced land. Whenever three cells of a 2×2 square are already shaded, the fourth cell must be white — it cannot be sea without breaking the rule, so it belongs to an island even before you know which one. Keep glancing at every two-by-two window as you shade; the moment one is three-quarters water, you have found a guaranteed island cell for free. This trick is especially powerful in open regions far from any clue, where it is often the only thing that tells you where land has to appear.
Keep the water flowing as one
All the sea must connect, so watch for cells that would strand a pocket of water or a would-be island with no way out. If shading a cell would seal off a lone sea cell from the rest of the ocean, that cell must instead stay white; if leaving a cell white would trap the sea, it must be shaded. Late in a puzzle, when most of the board is settled, connectivity becomes the decider — ask of each undecided cell, "does the sea still reach everywhere if I shade this, and does every island still have room to breathe if I don't?" On vygam you can press Check at any point to flash any broken rule in red, which is a fast way to confirm a chain of reasoning before you commit to it.
Difficulty Levels & Puzzles
vygam ships Nurikabe in three tiers, and every board is authored by hand and then checked by machine against all four rules so its solution is guaranteed valid. Easy puzzles use a compact 5×5 grid with small islands, so the "cells around a 1 are sea" and "size rule" deductions carry you smoothly from clue to clue. They are the perfect place to get a feel for how land and water constrain each other before the connectivity and no-2×2 rules ever become tricky, and to build up speed reading the board at a glance.
Medium puzzles step up to a 7×7 grid with more islands and longer chains of reasoning, so you lean harder on counting each clue's reach and on watching the sea stay connected across the whole board. Hard puzzles fill a full 9×9 grid, where the no-2×2 rule and sea connectivity frequently become essential to place the final cells, and where a single early deduction can cascade across the map. Your fastest completion is saved separately for each difficulty right in your browser, so you can chase a personal best on the 5×5 boards while working your way up to the 9×9 set. Tap New puzzle any time to move to the next board in the current tier — the collection cycles, so there is always another coastline waiting to be drawn.
Nurikabe vs Sudoku, Nonogram & Other Logic Puzzles
If you enjoy Sudoku, Nonogram, Hitori or Slitherlink, Nurikabe will feel like a close cousin with its own distinct flavour. Like all of them it is a pure deduction puzzle with a single logical answer and no math beyond simple counting, and like Nonogram and Hitori it is solved by shading cells rather than writing digits. But where Nonogram uses numeric clues to reveal a hidden picture and Hitori shades away duplicate numbers, Nurikabe asks you to sculpt a whole two-tone map — land and water — in which the shaded cells and the white cells constrain each other by shape and connection, not just by value.
That focus on connected regions is what sets Nurikabe apart. Sudoku and Hitori care about what appears in a line; Slitherlink cares about a single closed loop; Nurikabe cares about the geometry of islands and a sea, with rules that read almost like a description of a real coastline. The result is a puzzle that rewards spatial imagination as much as arithmetic-free logic, which is why it has spread from Nikoli's magazines into puzzle books and apps around the world — and why it plays so well as a short, absorbing thinking break right in your browser.
FAQ
Is Nurikabe free to play?
Yes — Nurikabe on vygam is completely free and plays instantly in your browser. There is no download and no sign-up; you can play Easy, Medium and Hard puzzles on phone, tablet or desktop whenever you like.
How do you play Nurikabe?
You start with a grid holding a few numbered cells and you shade the other cells to form the sea, leaving the rest white as islands. Tap a blank cell to shade it and tap again to clear it; numbered cells are locked and can never be shaded. Shade so that every island is one connected group containing exactly one number that equals how many cells the island has, islands never touch edge to edge, the whole sea is joined into one region, and no 2x2 area is completely shaded.
What are the rules of Nurikabe?
Nurikabe has four rules that must all hold at once. First, every island — an orthogonally-connected group of white cells — must contain exactly one number, and that number equals the island's cell count. Second, two islands may never touch horizontally or vertically, though they may meet at a diagonal corner. Third, all the shaded sea cells must form a single connected region. Fourth, the sea may never contain a 2x2 block of four cells that are all shaded. A grid where all four rules are satisfied is solved.
Where does Nurikabe come from?
Nurikabe was popularised by the Japanese puzzle publisher Nikoli, the same company behind Sudoku's rise, and it first appeared in their magazines in the early 1990s. The name comes from a yokai, a creature of Japanese folklore said to be an invisible wall that blocks travellers at night, which fits the puzzle's theme of a spreading wall of water hemming in small islands of dry land.
Does Nurikabe require math?
No. The numbers are only island sizes, so the only counting you ever do is checking that an island has as many white cells as its clue says. There is no arithmetic, no addition and no subtraction — Nurikabe is a pure logic puzzle solved by deduction about which cells must be sea and which must be land, much like Sudoku, Nonogram or Hitori.