This Penrose Slitherlink puzzle is inspired by David Millar’s “Area 51″ puzzles, which you can find at The Griddle. The puzzle works like a regular Slitherlink puzzle, but with a few twists: The aliens must be kept inside the fence. The cacti must be kept outside the fence. The white circles indicate a straight line crossing.
Special thanks to David Millar, who drew the cacti and aliens.