Nurikabe is a binary determination puzzle. You must decide for each cell if it is white or black (by clicking on them) according to the following rules:
- All of the black cells must be connected.
- Each numbered cell must be part of a white island of connected white cells.
- Each island must have the same number of white cells as the number it contains (including the numbered cell).
- Two islands may not be connected.
- There cannot be any 2x2 blocks of black cells.
Read more about the history and methods behind nurikabe in the Wikipedia nurikabe article.