Lighthouses is played on a rectangular or square grid. It contains black cells with numbers ("lighthouses"). The number in the cell represents the number of ships lit by the lighthouse. A ship is lit if it is in the same row or column as the lighthouse, also ships behind other ships or lighthouses. Each ship is lit by at least one lighthouse. The ships are placed so that no ship touches any other ship or lighthouse, not even diagonally.
Cross+A can solve puzzles from 4 x 4 to 20 x 20.