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Nurikabe
Nurikabe is a binary-determination puzzle by Nikoli, named after a mythical Japanese wall-spirit. You shade cells to create a "sea" of wall around "islands" of clear cells. Each numbered clue defines the size of one island, and the rest of the grid becomes connected wall.
Nurikabe Rules
Each number on the grid is the size of an island — a group of unshaded cells, connected horizontally or vertically, containing exactly that many cells including the clue itself. Every island holds exactly one number.
All remaining cells are shaded to form the wall (the sea). The entire wall must be a single connected group, and it may never contain a filled 2×2 block of shaded cells anywhere.
Islands cannot touch each other horizontally or vertically — they may only meet diagonally, separated by wall. When every island is the right size, walled off from the others, and the sea is one connected, block-free region, the puzzle is solved uniquely.
Nurikabe Strategy & Tips
Wall off cells between close clues
A cell sandwiched between two different numbered islands can't belong to either, so it must be sea. Shading these separators early prevents islands from merging.
Surround completed islands
Once an island reaches its target size, shade every cell around its border. This both seals the island and feeds the connected wall you're building.
Avoid the 2×2 wall trap
The sea can never form a solid 2×2 square. If three cells of a square are shaded, the fourth must be an island cell — a powerful deduction to force island growth.
Keep the sea connected
Walls must all link up. If shading would strand a pocket of sea, that move is illegal, so the alternative cell must instead be part of an island.
Frequently Asked Questions
What do the numbers mean in Nurikabe?
Each number is the exact size, in cells, of the island it belongs to. Every island contains one number and that many connected unshaded cells.
Can shaded cells form a 2×2 block in Nurikabe?
No. The wall may never contain a solid 2×2 square of shaded cells anywhere on the grid.
Can two islands touch in Nurikabe?
Not edge to edge. Islands may only touch diagonally; they must be separated by wall along all horizontal and vertical borders.
What does Nurikabe mean?
Nurikabe is named after a yokai from Japanese folklore — an invisible wall-spirit that blocks travelers' paths, fitting the puzzle's connected wall theme.