Unreachable Square

Sometimes, a square can be classified as a wall or an island based on its accessibility from other squares. If a square is unreachable by any island or wall, it must be classified as the opposite.

Consider the following example:

In this situation, the highlighted square is unreachable by the existing islands. As such, it cannot be an island square and must therefore be a wall square.

Understanding the concept of unreachable squares is critical to mastering more complex Nurikabe puzzles. Always keep an eye on isolated squares and evaluate their reachability!