If take your car to the bottom of a certain hill of Springer, Oklahoma you will experience one of the strangest phenomena. Cars in neutral and bicyclists will start rolling up the hill in clear defiance of gravity. This is known as a magnetic hill or mystery hill and there are hundreds of related phenomena across the globe. It is up to debate whether the causes for this lapse in gravity are all the same.
There are many theories as to how this can happen, including aliens, ghosts, and optical illusions. The optical illusion theory is interesting. The layout of the surrounding land confuses the viewer into seeing a downward slope as upward. The illusion is consistent with a obstructed horizon. With out a reliable reference the eye can be easily fooled. Sometimes, for varying reasons objects like trees may be leaning but viewed as perpendicular to the earth. This would tilt any perspective. Like I was saying there are many of these hills throughout the world. This means you may not have to go to Oklahoma to experience this event.
My friend has been to one such in the Philippines, and reports that he saw water flow up a hill. I explained to him the optical illusion theory of why this occurs. He replied that this hill was surrounded by nothing besides a few houses. He could clearly see the horizon. I have no explanation to this. The experts seem to be similarly stunned.