A gravity hill, also known as a magnetic hill and sometimes a mystery hill, a mystery spot, or a gravity road, is a place where the layout of the surrounding land produces the optical illusion that a very slight downhill slope appears to be an uphill slope. Thus, a car left out of gear will appear to be rolling uphill due to gravity.
The slope of gravity hills is an optical illusion, although sites are often accompanied by claims that magnetic or even supernatural forces are at work.
The most important factor contributing to the illusion is a completely or mostly obstructed horizon; without a horizon, judging the slope of a surface is difficult as a reliable reference is missing.
One such magnetic hill can be seen at Peterborough in South Australia. The hill and it’s illusion is treated with some levity by the locals. The effect when visited is quite marked and best viewed from the supposed uphill position.