Nurikabe

Build islands and seas on a grid. Numbered cells show the size of each island. The black cells form a single sea with no 2×2 pools.

Click a cell to cycle: unknown → black (sea) → white (island) → unknown. Numbered cells are fixed island cells and cannot be toggled.

Try to form white islands of the indicated sizes, surrounded by a single connected sea of black cells with no 2×2 black blocks.

What is Nurikabe?

Nurikabe is a Japanese logic puzzle about islands and sea. The numbered cells are islands, and the black cells form the sea. Each number tells you how many white cells belong to that island.

How to play

Each number is part of a white island of exactly that many orthogonally connected white cells.
Every island contains exactly one number; islands cannot touch horizontally or vertically (only diagonally).
Black cells form the sea. All black cells must be connected in one group, with no 2×2 block of black cells.
When all islands and sea rules are satisfied, the puzzle is solved.

Controls

Click an empty cell to cycle: unknown → black (sea) → white (island) → unknown.
Numbered cells are fixed white cells (island cores) and cannot be changed.
Red outlines highlight sea errors; amber outlines highlight island issues while you experiment.

Beginner tips

Large numbers usually force several neighbours to be white to reach the required island size.
Whenever a 2×2 block of potential black cells appears, at least one of them must stay white.
Use the connectivity rule: avoid cutting the sea into separated lakes as you mark black cells.