Nurikabe guide
How to solve Nurikabe
Nurikabe splits a grid into islands and sea. Every board has exactly one solution, and five small ideas get you there. These are the lessons from Insula, the app, played right here on the page.
The rules
- Split the grid into land and sea.
- Every number belongs to an island of exactly that many cells.
- Every island contains exactly one number.
- Islands never touch left, right, up or down. Corners are fine.
- All the sea is one connected body.
- The sea never fills a whole 2x2 block.
What a solved board looks like
Tap a cell to mark it sea, tap again to clear it. Long-press to mark it land. Drag to mark a run.
1A finished island
The 1 at the bottom is already a whole island: one cell, and that is all it is allowed. So what has to be around it? Mark the three neighbouring cells — tap a cell to make it sea.
2Two numbers never share an island
Two 3s, with one cell between them. What must that cell be?
3The only way to grow
The 3 in the corner has only one cell so far, so it still has to grow. Where is the only place left for it to go? — press and hold a cell to make it land.
4No 2×2 block of sea
These three cells are sea. What would happen if the fourth one were sea as well?
5The sea stays in one piece
The sea cell in the corner is boxed in. It still needs a way out to the rest of the sea.
6A whole board
Now a whole board. Use everything above — and the hint button if you get stuck, which explains itself the same way this walkthrough did.
That is the whole game
Five ideas: an island is as big as its number, two numbers never meet, an island with one way out takes it, the sea never forms a 2x2 block, and the sea stays in one piece.
That is all the theory a board needs. The big ones are the same five ideas, many moves deep.