How to Solve Nurikabe: Islands, the Wall, and the No-Pool Rule

Updated August 2026

Nurikabe asks you to paint a grid so that every numbered cell grows into an island of exactly that size, and everything you paint forms one connected wall with no 2×2 block anywhere. Two things trip up newcomers: they focus only on the islands and forget the wall is also a puzzle, and they miss how much can be deduced from cells that no island could ever reach.

The rules, stated precisely

• Each number is part of exactly one island of unpainted cells whose size equals that number.
• Every island contains exactly one number, and islands never touch each other edge to edge.
• All painted cells form a single connected wall.
• The wall never contains a 2×2 painted block.

Separate first, grow later

Before extending anything, look for cells that sit orthogonally between two different numbers. Such a cell can belong to neither island, because joining it to one would touch the other. Paint it. Diagonal neighbours of two numbers are the same idea: the single cell that would connect them must be wall. Sweeping every pair of nearby numbers this way often paints a surprising fraction of the board before you have grown a single island.

A 1 is finished the moment you see it. All four of its neighbours are wall, immediately and without further thought. Clearing every 1 on the board is the cheapest opening move in the game.

Unreachable cells are wall

This is the technique that separates casual solvers from fast ones. For each unpainted cell, ask whether any numbered island could legally reach it. Count the walking distance from each number, remembering that an island of size n can extend at most n − 1 steps from its clue, and that the path cannot pass through wall or through another island. If no number can reach the cell, it must be wall. Painting all unreachable cells after each round of growth is the single highest-yield sweep in Nurikabe, and it is purely mechanical — no creativity required.

The no-2x2 rule cuts both ways

Everyone remembers that four painted cells may not form a square. Fewer people use it as a positive tool. If three cells of a 2×2 block are already wall, the fourth is guaranteed to be part of some island — leave it unpainted, and then work out which island can reach it. That forced island cell frequently gives an island its only possible growth direction, which in turn lets you fence the island's completed border with wall.

Keep the wall breathing

Because the wall must be one connected region, any painted cell or group with a single remaining escape route forces that route to be painted. Watch for wall segments that are about to be sealed off by islands: if a painted area has exactly one unpainted neighbour left through which it can ever join the rest of the wall, that neighbour is wall. Late in a puzzle this constraint usually resolves the last few ambiguous cells on its own.

Fence every completed island

The instant an island reaches its number, paint its entire border. This is easy to forget when you are absorbed in a different corner, and it is free information: a fenced island shrinks the reachable area for every other clue, which feeds straight back into the unreachable-cell sweep.

A reliable order of attack

1. Fence every 1.
2. Paint cells trapped between two clues, orthogonally and diagonally.
3. Grow any island that has exactly one legal direction.
4. Fence every island that has reached its size.
5. Sweep for unreachable cells and paint them.
6. Apply the 2×2 rule in both directions, then check wall connectivity.
7. Repeat from step 3 until the board is finished.

A well-made Nurikabe is solvable entirely by these steps. When you feel stuck, the answer is nearly always another unreachable-cell sweep — the board has changed since your last one, and cells that were reachable ten moves ago may not be any more.