1. The object is to create a single loop that will pass through every country. The yellow lines are the borders of those countries.
2. Within each country, the line/loop can only pass through a Sun or Moon. When going from country to country, the sun & moon must alternate. Also, within a single country, you can pass through multiple suns or multiple moons, but not both.
I like this game a lot. I did all the 5x5 grids quickly, then jumped to the 10x10 levels. And that's when I noticed a bug in the program. No matter what loop I draw, the program says I've solved it. Oh well. It's still a good game and you know when you've solved it or when you're stuck.