How to play Nurikabe

A map puzzle. Every number is an island of that many white cells. Shade the rest as sea, keeping the sea in one piece with no 2×2 pools.

The rules

Each number belongs to one island: a group of white cells joined side by side, with exactly that many cells (counting the number).
Every island has exactly one number, and islands never touch side by side.
All shaded cells (the sea) are connected side by side.
The sea never has a 2×2 block of shaded cells.

Here is a small Nurikabe puzzle being solved one step at a time. Press Play, or use Back and Next to go at your own pace.

Press Play to start.

Tap a cell to shade it as sea. Switch to “Island dot” to mark cells you know are land.

A 1 is an island on its own, so shade all four of its neighbors.

A cell between two different numbers must be sea, because islands can’t touch.

Count: the sea is every cell that isn’t part of an island. Add up the numbers to know how many white cells there are.
Look for 2×2 squares with three shaded cells: the fourth must be land.
Cells that no island can reach are always sea.