Gravity Hill – A hill that gives the illusion of objects rolling uphill

A gravity hill, also known as a magnetic hill (and sometimes a mystery hill 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. There are hundreds of gravity hill locations around the world.

The slope of gravity hills is an optical illusion, although tour guides may claim natural 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. Objects one would normally assume to be more-or-less perpendicular to the ground (such as trees) may actually be leaning, offsetting the visual reference. The illusion is similar to the well-known Ames room, in which balls can also appear to roll against gravity.

Websites devoted to the paranormal also tend to have names like “Haunted Hill”, “Magnetic Hill”, or “Anti-gravity Hill”, reflecting attribution of the properties of the area to the supernatural or magnetism. While humans also have a sense of balance to determine the inclination of the ground, visual cues can override this sense, especially if the inclination is shallow.