If a car were sitting where the kids are standing, would it roll toward you or away? Duh, you know it’s an optical illusion, so the car must roll away. But that’s pretty freaky, huh? Because most foothills slope up toward the mountains, our brain expects these foothills to do the same. Nope. The keys to this illusion are a mostly obscured horizon and lack of trees or other vertical visual clues. This downward slope as upward slope illusion is known as a gravity hill. A quick Internet search returns the locations of hundreds of gravity hills around the world.