Golem Grad

Golem Grad (an island in Lake Prespa, in the Republic of North Macedonia) combines the rules of Nurikabe and Snake puzzles. A rectangular or square grid contains circles and numbers in some cells. The aim is to blacken some cells according to the following rules:

• The black cells divide the grid into areas of white cells ("islands"), each containing at most one number.
• Two islands may not be connected.
• The island must have the same number of white cells as the number it contains.
• All black cells must form an orthogonally continuous area.
• No 2 x 2 cell area within the grid can have the black color.
• All black cells must be divisible into "snakes" with the heads and tails given as circles in the grid.
• Snakes must not cross each other.

Cross+A can solve puzzles from 3 x 3 to 30 x 30.