They said the fortress of the evil warlord was impregnable: stone walls sixteen feet thick, infrared security cameras and motion detectors, enemy soldiers with machine guns, attack dogs, tanks, aircraft, etc, etc. The works. They said no one could ever get in, rescue the kidnapped princess, assassinate the warlord, and get out in one piece.
Of course, they never reckoned on The Bulldog...
Notes
This game was a 2006 Xyzzy Awards Finalist in the category "Best Puzzles".